Closes https://github.com/curl/curl/pull/1028

LibreSSL defines `OPENSSL_VERSION_NUMBER` as `0x20000000L` for all
versions returning `LibreSSL/2.0.0` for any LibreSSL version.

This change provides a local OpenSSL_version_num function replacement
returning LIBRESSL_VERSION_NUMBER instead.

Closes #1029

Closes #1025
Closes #1026
Closes #1027

Follow-up fix to d9321562

The OpenSSL function CRYTPO_cleanup_all_ex_data() cannot be called
multiple times without crashing - and other libs might call it! We
basically cannot call it without risking a crash. The function is a
no-op since OpenSSL 1.1.0.

Not calling this function only risks a small memory leak with OpenSSL <
1.1.0.

Bug: https://curl.haxx.se/mail/lib-2016-09/0045.html
Reported-by: Todd Short

RC4 was a nice alternative to CBC back in the days of BEAST, but it's insecure and obsolete now.

Since I first wrote that text, Apple introduced tvOS and watchOS, and renamed "Mac OS X" to "macOS." Let's make the text a little more inclusive, since curl can be built for all four operating systems.

Prior to this commit this example failed with error
'Cannot APPEND with unknown input file size'.

Bug: https://github.com/curl/curl/issues/1008


Reported-by:  <lukaszgn@users.noreply.github.com>

Closes https://github.com/curl/curl/pull/1011

Recent versions of mbedTLS are available under either Apache 2.0 or GPL
2.0, see https://tls.mbed.org/how-to-get

Closes #1019

... but don't send the actual header over the wire as it isn't accepted.
Chunked uploading is still triggered using this method.

Fixes #1013
Fixes #662

OpenSSL 1.0.1 and 1.0.2 build an error queue that is stored per-thread
so we need to clean it when easy handles are freed, in case the thread
will be killed in which the easy handle was used. All OpenSSL code in
libcurl should extract the error in association with the error already
so clearing this queue here should be harmless at worst.

Fixes #964

CVE-2016-7167

Bug: https://curl.haxx.se/docs/adv_20160914.html

CVE-2016-7167

Bug: https://curl.haxx.se/docs/adv_20160914.html

Reported-by: Ryan Scott

Fixes #1007

NTLM support with mbedTLS was added in 497e7c9d but requires that mbedTLS
is built with the MD4 functions available, which it isn't in default
builds. This now adapts if the funtion isn't there and builds libcurl
without NTLM support if so.

Fixes #1004

- Change maximum allowed line length from 80 to 79.

Note that since the added examples are for column alignment I had to
encapsulate with ~~~c markdown to preserve their alignment.

The `curl-config --static-libs` command should not output paths like
-l/usr/lib/libssl.so, instead print the absolute path without `-l`.

This also removes the confusing message "Static linking is broken" which
was printed because curl-config --static-libs was disfunctional even
though the static libcurl.a library works properly.

Fixes https://github.com/curl/curl/issues/841

... like when a HTTP/0.9 response comes back without any headers at all
and just a body this now prevents that body from being sent to the
callback etc.

Adapted test 1144 to verify.

Fixes #973

Assisted-by: Ray Satiro

This only excludes building unit tests from default build ( 'all' Make
target or "Build Solution" in VisualStudio). The projects and Make
targets will still be generated and shown in supporting IDEs.

Fixes https://github.com/curl/curl/issues/981
Reported-by: Randy Armstrong

Closes https://github.com/curl/curl/pull/990

Detect support for compiler symbol visibility flags and apply those
according to CURL_HIDDEN_SYMBOLS option.
It should work true to the autotools build except it tries to unhide
symbols on Windows when requested and prints warning if it fails.

Ref: https://github.com/curl/curl/issues/981#issuecomment-242665951
Reported-by: Daniel Stenberg

... by partially reverting f975f060. The allocation could be made by
OpenSSL so the free must be made with OPENSSL_free() to avoid problems.

Reported-by: Harold Stuart
Fixes #1005

... by making sure we don't count down the "upload left" counter when the
uploaded size is unknown and then it can be allowed to continue forever.

Fixes #996

Since we're using CURLE_FTP_WEIRD_SERVER_REPLY in imap, pop3 and smtp as
more of a generic "failed to parse" introduce an alias without FTP in
the name.

Closes https://github.com/curl/curl/pull/975

... as that function slipped through once before.

This hash is used to verify the original downloaded certificate bundle
and also included in the generated bundle's comment header. Also
rename related internal symbols to algorithm-agnostic names.