curlx/fopen: replace open CRT functions their with _s counterparts (Windows)

[vszakats]

• _wopen -> _wsopen_s
• _open, open -> _sopen_s
• _wfopen -> _wfopen_s
• fopen -> fopen_s
• _wfreopen -> _wfreopen_s
• freopen -> freopen_s

For better error handling and for using the CRT functions recommended
via warnings suppressed by _CRT_SECURE_NO_WARNINGS.

Also:

• add missing freopen_s() prototype when building with mingw-w64 <5.
  https://sourceforge.net/p/mingw-w64/mingw-w64/ci/a5d824654cdc57f6eac1bb581b078986f3eb6856/
• tests/server: replace open() in the signal handler with _sopen_s()
  on Windows.
• tests/server: reduce scope of a checksrc exception to a single line.
• checksrc: ban replaced functions.

Refs:
https://learn.microsoft.com/cpp/c-runtime-library/reference/open-wopen
https://learn.microsoft.com/cpp/c-runtime-library/reference/sopen-s-wsopen-s
https://learn.microsoft.com/cpp/c-runtime-library/reference/freopen-wfreopen
https://learn.microsoft.com/cpp/c-runtime-library/reference/fopen-wfopen
https://learn.microsoft.com/cpp/c-runtime-library/reference/fopen-s-wfopen-s
https://learn.microsoft.com/cpp/c-runtime-library/reference/freopen-s-wfreopen-s

---

• use freopen_s with mingw-w64 5+ only.
• rename lib/share.h to avoid collision with CRT share.h. → lib: rename internal header share.h to curl_share.h to avoid collision #19676
• #include <share.h> includes lib/share.h instead of share.h from the CRT.
  Ref: lib: include files using known path #16991 that seemed fixing this issue reported in share.h conflicts with windows ucrt header #16949, but apparently this
  use-case still hits it. Avoiding the name collision by renaming would be best?
• test failures. I still got something wrong about the update that makes some tests
  fail, some others time out. → curl_fopen: do not pass invalid mode flags to open() on Windows #19645
• after the above: TESTFAIL: These test cases failed: 204 1490 (file:// protocol upload)
  Finalize the rough/quick fix, to try honoring data->set.new_file_perms.
  Also split to separate PR. → file: do not pass invalid mode flags to open() on upload (Windows) #19647
• bump minimum to mingw-w64 v4 (2015-03-05) to avoid adding a new exception? (and dropping an existing one) → sep PR → turns out v5 is the minumum required. Went with a different solution, by adding the missing prototype to curl sources for <=v4.
  Proposal: Bump required mingw-w64 version to 3.0 (from 1.0) #17984
• rebase on curl_fopen: do not pass invalid mode flags to open() on Windows #19645
• rebase on file: do not pass invalid mode flags to open() on upload (Windows) #19647
• rebase on vquic: do not pass invalid mode flags to open() (Windows) #19670
• rebase on tftpd: fix/tidy up open() mode flags #19671
• tftpd: replace open() call with curlx_open(). → tests/server: use curlx file open/close functions #19679
• tests/server: replace fopen() call with curlx_fopen(). → tests/server: use curlx file open/close functions #19679
• servers/util: replace open() call with _s variant on Windows.
• review code for other potential invalid open flags.
• and/or perhaps filter them right before the CRT call? [SKIPPED]

[vszakats]

Issues:

• freopen_s requires mingw-w64 4+.
• #include <share.h> includes lib/share.h instead of share.h from the CRT.
  Ref: lib: include files using known path #16991 that seemed fixing this issue reported in share.h conflicts with windows ucrt header #16949, but apparently this
  use-case still hits it. Avoiding the name collision by renaming would be best?
• test failures. I still got something wrong about the update that makes some tests
  fail, some others time out.
  → Caused by passing invalid pmode flags to open on Windows
• after the above: TESTFAIL: These test cases failed: 204 1490 (file:// protocol)

[vszakats]

Fine, pytests broken (test_17_ssl_use, 20 variants failed) after Homebrew bumped wolfSSL to 5.8.4 (from previous release 5.8.2):
BAD: https://github.com/curl/curl/actions/runs/19582773452/job/56084526466
GOOD: https://github.com/curl/curl/actions/runs/19575732267

SSL_connect failed with error -311: unknown type in record hdr

https://github.com/wolfSSL/wolfssl/releases/tag/v5.8.4-stable

→ #19644

[vszakats]

TL;DR the reason for the CI failures seen earlier in #19581 (comment) were:

• missed passing _SH_DENYNO (or other valid values) to open().
• pre-existing code passing invalid mode flags to open().

These were addressed in this PR and a series of separate commits today.

[vszakats]

CRT functions flagged by _CRT_SECURE_NO_WARNINGS after this patch:

• 39 'strcpy' (lib, src, curlx, libtests, servers) → strcpy_s
• 21 'getenv' (lib, src, libtests) → _dupenv_s
• 18 'sscanf' (1x libtests, servers) → sscanf_s
• 3 'localtime' (src, libtests, servers) → localtime_s
• 2 'gmtime' (lib, src) → gmtime_s
• 1 'sprintf' (curlx) → sprintf_s → curlx: replace sprintf with snprintf #19681