Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

This reduces the GCC job runtimes a little and it's needed to
selectively update clang builds to xenial.

Closes https://github.com/curl/curl/pull/3721

Closes https://github.com/curl/curl/pull/3725

- remove unused variables
- declare conditionally used variables conditionally
- suppress unused variable warnings in the CMake tests
- remove dead variable stores
- consistently use WIN32 macro to detect Windows

Closes https://github.com/curl/curl/pull/3739

Make functions no-ops if neither both USE_THREADS_POSIX and
HAVE_PTHREAD_H nor both USE_THREADS_WIN32 and HAVE_PROCESS_H are
defined. Previously, if only one of them was defined, there was either
code compiled that did nothing useful or the wrong header included for
the functions used.

Also, move POLARSSL_MUTEX_T define to implementation file as it's not
used externally.

Closes https://github.com/curl/curl/pull/3739

These variables are only conditionally initialized.

Closes https://github.com/curl/curl/pull/3739

Closes https://github.com/curl/curl/pull/3739

Consistently use one blank line between blocks.

Closes https://github.com/curl/curl/pull/3739

Always use the ANSI version of FormatMessage as we don't have the
curl_multibyte gear available here.

Closes https://github.com/curl/curl/pull/3758

The stripcredentials unittest fails to compile on platforms without
xattr support, for example the Solaris member in the buildfarm which
fails with the following:

  CC unit1621-unit1621.o
  CC ../libtest/unit1621-first.o
  CCLD unit1621
  Undefined first referenced
  symbol in file
  stripcredentials unit1621-unit1621.o
  goto problem 2
  ld: fatal: symbol referencing errors. No output written to .libs/unit1621
  collect2: error: ld returned 1 exit status
  gmake[2]: *** [Makefile:996: unit1621] Error 1

Fix by excluding the test on such platforms by using the reverse
logic from where stripcredentials() is defined.

Closes #3759
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

Stick to "Schannel" everywhere - follow up to 180501cb.

This fixes GSSAPI builds with the libraries in a non-standard location.
The testing for recv() were failing because it failed to link
the Kerberos libraries, which are not needed for this or subsequent
tests.

fixes #3743
closes #3744

With CMAKE_TRY_COMPILE_TARGET_TYPE set to STATIC_LIBRARY, the try_compile()
(which is used by check_c_source_compiles()) will build static library
instead of executable. This avoids linking additional libraries in and thus
speeds up those checks a little.

This commit also avoids #3743 (GSSAPI build errors) on itself with cmake
3.6 or above. That issue was fixed separately for all versions.

Ref: #3744

- Remove nneeded include_regular_expression.
  It was setting what is already a default.

- Remove duplicated include.

- Don't check for pre-3.0.0 CMake version.
  We already require at least 3.0.0, so it's just clutter.

Ref: #3744

Should the parent environment set this variable then the build might
not be performed as the user intended.

Fixes #3738
Closes #3749

bumped to 7.65.0 for next release

bytes... since the protocol needs to store the length in a single byte field.

Reported-by: XmiliaH on github
Fixes #3737
Closes #3740

fixes #3741
Closes #3742

Fixes #3745
Closes #3746

The following snippet
```

int main()
{
    CURL* hCurlHandle = curl_easy_init();
    curl_easy_setopt(hCurlHandle, CURLOPT_URL, "http://example.com");
    curl_easy_setopt(hCurlHandle, CURLOPT_PROXY, "1");
    curl_easy_perform(hCurlHandle);
    curl_easy_cleanup(hCurlHandle);
    return 0;
}
```
triggers the following Valgrind warning

```
==4125== Invalid read of size 8
==4125==    at 0x4E7D1EE: Curl_llist_remove (llist.c:97)
==4125==    by 0x4E7EF5C: detach_connnection (multi.c:798)
==4125==    by 0x4E80545: multi_runsingle (multi.c:1451)
==4125==    by 0x4E8197C: curl_multi_perform (multi.c:2072)
==4125==    by 0x4E766A0: easy_transfer (easy.c:625)
==4125==    by 0x4E76915: easy_perform (easy.c:719)
==4125==    by 0x4E7697C: curl_easy_perform (easy.c:738)
==4125==    by 0x4008BE: main (in /home/even/curl/test)
==4125==  Address 0x9b3d1d0 is 1,120 bytes inside a block of size 1,600 free'd
==4125==    at 0x4C2ECF0: free (vg_replace_malloc.c:530)
==4125==    by 0x4E62C36: conn_free (url.c:756)
==4125==    by 0x4E62D34: Curl_disconnect (url.c:818)
==4125==    by 0x4E48DF9: Curl_once_resolved (hostip.c:1097)
==4125==    by 0x4E8052D: multi_runsingle (multi.c:1446)
==4125==    by 0x4E8197C: curl_multi_perform (multi.c:2072)
==4125==    by 0x4E766A0: easy_transfer (easy.c:625)
==4125==    by 0x4E76915: easy_perform (easy.c:719)
==4125==    by 0x4E7697C: curl_easy_perform (easy.c:738)
==4125==    by 0x4008BE: main (in /home/even/curl/test)
==4125==  Block was alloc'd at
==4125==    at 0x4C2F988: calloc (vg_replace_malloc.c:711)
==4125==    by 0x4E6438E: allocate_conn (url.c:1654)
==4125==    by 0x4E685B4: create_conn (url.c:3496)
==4125==    by 0x4E6968F: Curl_connect (url.c:4023)
==4125==    by 0x4E802E7: multi_runsingle (multi.c:1368)
==4125==    by 0x4E8197C: curl_multi_perform (multi.c:2072)
==4125==    by 0x4E766A0: easy_transfer (easy.c:625)
==4125==    by 0x4E76915: easy_perform (easy.c:719)
==4125==    by 0x4E7697C: curl_easy_perform (easy.c:738)
==4125==    by 0x4008BE: main (in /home/even/curl/test)
```

This has been bisected to commit 2f44e94e

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=14109
Credit to OSS Fuzz

As previously planned and documented in DEPRECATE.md, all pipelining
code is removed.

Closes #3651

Closes #3731
Fixes #3289

This groups all SSL backends into the feature "SSL" and sets the
SSL_BACKENDS analogue to configure.ac

Closes https://github.com/curl/curl/pull/3736

In case of an empty list, SORTing leads to the cmake error "list
sub-command SORT requires list to be present."

Closes https://github.com/curl/curl/pull/3736

Fish defines a vendor completions directory for completions that are not
installed as part of the fish project itself, and the vendor completions
are preferred if they exist. This prevents trying to overwrite the
builtin curl.fish completion (or creating file conflicts in distro
packaging).

Prefer the pkg-config defined location exported by fish, if it can be
found, and fall back to the correct directory defined by most systems.

Closes #3723
Reviewed-by: Daniel Gustafsson

Removing the block is consistent with line 954/957.

Closes https://github.com/curl/curl/pull/3732

Just remove the redundant condition, which also makes it clear that
k->buf is always 0-terminated if this break is not hit.

Closes https://github.com/curl/curl/pull/3732

- Fix clang string-plus-int warning.

Clang 8 warns about adding a string to an int does not append to the
string. Indeed it doesn't, but that was not the intention either. Use
array indexing as suggested to silence the warning. There should be no
functional changes.

(In other words clang warns about "foo"+2 but not &"foo"[2] so use the
latter.)

smtp.c:1221:29: warning: adding 'int' to a string does not append to the
string [-Wstring-plus-int]
      eob = strdup(SMTP_EOB + 2);
            ~~~~~~~~~~~~~~~~^~~~

Closes https://github.com/curl/curl/pull/3729