[clang] [Clang][Cygwin] Cygwin x86_64 should accept __stdcall (PR #158385)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-global-isel` running on `linaro-clang-aarch64-global-isel` while building `clang` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/125/builds/10357

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests/5/21' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-global-isel/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-669741-5-21.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=21 GTEST_SHARD_INDEX=5 /home/tcwg-buildbot/worker/clang-aarch64-global-isel/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests
--

Note: This is test shard 6 of 21.
[==========] Running 63 tests from 53 test suites.
[----------] Global test environment set-up.
[----------] 1 test from ClangdAST
[ RUN      ] ClangdAST.IsDeeplyNested
Built preamble of size 707616 for file /clangd-test/TestTU.cpp version null in 0.09 seconds
[       OK ] ClangdAST.IsDeeplyNested (115 ms)
[----------] 1 test from ClangdAST (115 ms total)

[----------] 1 test from BackgroundQueueTest
[ RUN      ] BackgroundQueueTest.Duplicates
[       OK ] BackgroundQueueTest.Duplicates (0 ms)
[----------] 1 test from BackgroundQueueTest (0 ms total)

[----------] 1 test from ClangdServerTest
[ RUN      ] ClangdServerTest.RespectsConfig
Config fragment: compiling <unknown>:0 -> 0x0000EC0494000C30 (trusted=false)
ASTWorker building file /clangd-test/foo.cc version null with command clangd fallback
[/clangd-test]
/usr/lib/llvm-14/bin/clang -DFOO=1 -- /clangd-test/foo.cc
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name foo.cc -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir /usr/lib/llvm-14/lib/clang/22 -D FOO=1 -internal-isystem /usr/lib/llvm-14/lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/foo.cc
Building first preamble for /clangd-test/foo.cc version null
Built preamble of size 817460 for file /clangd-test/foo.cc version null in 0.99 seconds
Config fragment: compiling <unknown>:0 -> 0x0000EC04940121F0 (trusted=false)
Config fragment: compiling <unknown>:0 -> 0x0000EC04940B1C60 (trusted=false)
ASTWorker running Definitions on version null of /clangd-test/foo.cc
Config fragment: compiling <unknown>:0 -> 0x0000EC0490000C30 (trusted=false)
ASTWorker building file /clangd-test/bar.cc version null with command clangd fallback
[/clangd-test]
/usr/lib/llvm-14/bin/clang -- /clangd-test/bar.cc
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name bar.cc -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir /usr/lib/llvm-14/lib/clang/22 -internal-isystem /usr/lib/llvm-14/lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/bar.cc
Building first preamble for /clangd-test/bar.cc version null
Built preamble of size 817380 for file /clangd-test/bar.cc version null in 0.21 seconds
Config fragment: compiling <unknown>:0 -> 0x0000EC0490012000 (trusted=false)
Config fragment: compiling <unknown>:0 -> 0x0000EC0490059630 (trusted=false)
ASTWorker running Definitions on version null of /clangd-test/bar.cc
[       OK ] ClangdServerTest.RespectsConfig (1242 ms)
[----------] 1 test from ClangdServerTest (1242 ms total)

[----------] 1 test from LSPTest
[ RUN      ] LSPTest.GoToDefinition
<<< initialize: {}
<-- initialize(0)
--> reply:initialize(0) 0 ms
...

```

</details>

https://github.com/llvm/llvm-project/pull/158385