CMake: set MSVC warning level to 4

[MarcelRaad]

The MSVC warning level defaults to 3 in CMake. Change it to 4, which is
consistent with the Visual Studio and NMake builds. Disable level 4
warning C4127 for the library to get a clean CURL_WERROR build.

Also, /WX got added twice to the compiler flags for the release build and not
at all for the debug build. Fix this by using CMAKE_C_FLAGS instead of
CMAKE_C_FLAGS_RELEASE and CMAKE_C_FLAGS_DEBUG.

[mention-bot]

@MarcelRaad, thanks for your PR! By analyzing the history of the files in this pull request, we identified @billhoffman, @Sukender and @jzakrzewski to be potential reviewers.

[bagder]

It seems this warning level causes numerous tests run by cmake to fail...

[MarcelRaad]

c:\projects\curl\lib\curl_setup_once.h(164): error C2061: syntax error: identifier 'Missing_definition_of_return_and_arguments_types_of_recv'

I can only imagine that my CMake configuration wasn't updated when I moved the warning suppression from the top-level CMakeLists.txt to the one in the lib directory and the recv detection code doesn't compile because of the warning. I'll try moving it back to the top-level directory.

[MarcelRaad]

Still the same problem:

-- Performing Test curl_cv_func_recv_test - Failed
-- Performing Test curl_cv_func_send_test - Failed

Strange that it works on my machine (with the Ninja generator, though) but not on AppVeyor. :-(

[MarcelRaad]

I could reproduce this now with the Visual Studio project file generator back-end (which I haven't got to build anything yet, but generating the CMake cache works). Strangely, it failed because of a level 1 warning with CURL_WERROR, so I split the commit fixing CURL_WERROR into new PR #1715 now. Maybe CMAKE_C_FLAGS is used for the configuration tests while CMAKE_C_FLAGS_DEBUG/CMAKE_C_FLAGS_RELEASE is not?

[MarcelRaad]

What's that Travis failure again....

test 1208...[FTP PORT download, no data conn and no transient negative reply]
 1208: protocol FAILED:
--- log/check-expected	2017-08-01 16:20:14.530239179 +0000
+++ log/check-generated	2017-08-01 16:20:14.530239179 +0000
@@ -5,3 +5,4 @@
 TYPE I[CR][LF]
 SIZE 1208[CR][LF]
 RETR 1208[CR][LF]
+QUIT[CR][LF]

My mobile Chrome doesn't want to show the AppVeyor log, I'll check tomorrow at my desktop computer.

[MarcelRaad]

test 1399...[Curl_pgrsTime unit tests]

unit1399 returned 1, when expecting 0
 exit FAILED
== Contents of files in the log/ dir after test 1399
=== Start of file stderr1399
 URL: -
 is 1000002 us same as 1 seconds? Yes
 is 1000002 us same as 1 seconds? Yes
 is 3000966 us same as 3 seconds? No
 unit1399.c:99 Assertion 'usec_matches_seconds(data.progress.t_starttransfer, 3)' failed: about 3 second should have passed
=== End of file stderr1399

[coveralls]

Coverage increased (+0.01%) to 75.335% when pulling 6a0d2ab on MarcelRaad:cmake_msvc_warnings into 7e48aa3 on curl:master.

[MarcelRaad]

Completely unrelated Travis failure again, test 2033 [NTLM connection mapping, pipelining enabled] for the newly added libressl job this time.

AppVeyor is happy now, so this is the version I would push. Unfortunately there were more evil macros than I thought, even using SIG_ERR always results in a warning under MSVC 11 (2012) because of a direct cast from 32-bit integer constant to 64-bit function pointer within the macro.