Fixes #2380

Detected by Coverity Analysis:

Error: IDENTIFIER_TYPO:
curl-7.58.0/tests/python_dependencies/impacket/spnego.py:229: identifier_typo: Using "SuportedMech" appears to be a typo:
* Identifier "SuportedMech" is only known to be referenced here, or in copies of this code.
* Identifier "SupportedMech" is referenced elsewhere at least 4 times.
curl-7.58.0/tests/python_dependencies/impacket/smbserver.py:2651: identifier_use: Example 1: Using identifier "SupportedMech".
curl-7.58.0/tests/python_dependencies/impacket/smbserver.py:2308: identifier_use: Example 2: Using identifier "SupportedMech".
curl-7.58.0/tests/python_dependencies/impacket/spnego.py:252: identifier_use: Example 3: Using identifier "SupportedMech" (2 total uses in this function).
curl-7.58.0/tests/python_dependencies/impacket/spnego.py:229: remediation: Should identifier "SuportedMech" be replaced by "SupportedMech"?

Closes #2379

Reported-by: Aron Bergman
Bug: https://curl.haxx.se/mail/lib-2018-03/0049.html

[ci skip]

This reverts commit a577059f.

The assignment really needs to be there or we risk working with an
uninitialized pointer.

follow-up to 72a0f625

To sync it with changes made for the libssh2 project.
Also cleanup some whitespace.

... don't consider it an error!

Assisted-by: Jay Satiro
Reported-by: Łukasz Domeradzki
Fixes #2365
Closes #2375

CVE-2018-1000121
Reported-by: Dario Weisser
Bug: https://curl.haxx.se/docs/adv_2018-97a2.html

Refuse to operate when given path components featuring byte values lower
than 32.

Previously, inserting a %00 sequence early in the directory part when
using the 'singlecwd' ftp method could make curl write a zero byte
outside of the allocated buffer.

Test case 340 verifies.

CVE-2018-1000120
Reported-by: Duy Phan Thanh
Bug: https://curl.haxx.se/docs/adv_2018-9cd6.html

CVE-2018-1000122
Bug: https://curl.haxx.se/docs/adv_2018-b047.html

Detected by OSS-fuzz

... and make sure to avoid integer overflows with really large values.

Reported-by: 刘佩东
Fixes #2371
Closes #2373

follow-up to e04417d9

Reported-by: Michael Kaufmann
Fixes #2357
Closes #2362

... as it is interesting for many users.

Closes #2349

Check for existence of import and static libraries with documented names
and use them if they do. Fallback to previous names.

According to
https://github.com/madler/zlib/blob/master/win32/README-WIN32.txt on
Windows, the names of the import library is "zdll.lib" and static
library is "zlib.lib".

closes #2354

gss_seal/gss_unseal have been deprecated in favor of
gss_wrap/gss_unwrap with GSS-API v2 from January 1997 [1]. The first
version of "The Kerberos Version 5 GSS-API Mechanism" [2] from June
1996 already says "GSS_Wrap() (formerly GSS_Seal())" and
"GSS_Unwrap() (formerly GSS_Unseal())".

Use the nondeprecated functions to avoid deprecation warnings.

[1] https://tools.ietf.org/html/rfc2078
[2] https://tools.ietf.org/html/rfc1964

Closes https://github.com/curl/curl/pull/2356

Added test 1265 that verifies.

Reported-by: steelman on github
Fixes #2353
Closes #2355

... so that the CI and more detects compiler warnings/errors properly!

Closes #2337

On MinGW and Cygwin, GCC and clang have been complaining about macro
redefinitions since 4272a0b0. Fix this
by undefining the macros before redefining them as suggested in
https://github.com/curl/curl/pull/2269.

Suggested-by: Daniel Stenberg

When targeting x64, MinGW-w64 complains about conversions between
32-bit long and 64-bit pointers. Fix this by reusing the
GNUTLS_POINTER_TO_SOCKET_CAST / GNUTLS_SOCKET_TO_POINTER_CAST logic
from gtls.c, moving it to warnless.h as CURLX_POINTER_TO_INTEGER_CAST /
CURLX_INTEGER_TO_POINTER_CAST.

Closes https://github.com/curl/curl/pull/2341

Update clang to version 3.9 and GCC to version 6.

Closes https://github.com/curl/curl/pull/2345

Fixes #2342