[OpenMP][libomp] Add OpenBSD, NetBSD and DragonFly stdarg handling (#…

…126182)

Fixes build on OpenBSD/aarch64.

```
FAILED: openmp/runtime/src/CMakeFiles/omp.dir/kmp_runtime.cpp.o
/home/brad/tmp/llvm-build/bin/clang++ --target=aarch64-unknown-openbsd7.6 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Domp_EXPORTS -I/home/brad/tmp/llvm-build/runtimes/runtimes-bins/openmp/runtime/src -I/home/brad/tmp/llvm-brad/openmp/runtime/src -I/home/brad/tmp/llvm-brad/openmp/runtime/src/i18n -I/home/brad/tmp/llvm-brad/openmp/runtime/src/include -I/home/brad/tmp/llvm-brad/openmp/runtime/src/thirdparty/ittnotify -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -fcolor-diagnostics -Wcast-qual -Wformat-pedantic -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -fno-semantic-interposition -fdata-sections -O3 -DNDEBUG -std=c++17 -fPIC   -D _GNU_SOURCE -D _REENTRANT -U_GLIBCXX_ASSERTIONS -UNDEBUG -fno-exceptions -fno-rtti -Wno-covered-switch-default -Wno-frame-address -Wno-strict-aliasing -Wno-switch -Wno-uninitialized -Wno-return-type-c-linkage -Wno-cast-qual -Wno-int-to-void-pointer-cast -MD -MT openmp/runtime/src/CMakeFiles/omp.dir/kmp_runtime.cpp.o -MF openmp/runtime/src/CMakeFiles/omp.dir/kmp_runtime.cpp.o.d -o openmp/runtime/src/CMakeFiles/omp.dir/kmp_runtime.cpp.o -c /home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1449:47: error: value of type 'kmp_va_list' (aka '__builtin_va_list') is not contextually convertible to 'bool'
 1449 |   return (master_th->th.th_teams_microtask && ap &&
      |                                               ^~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1449:44: error: invalid operands to binary expression ('microtask_t' (aka 'void (*)(int *, int *, ...)') and 'kmp_va_list' (aka '__builtin_va_list'))
 1449 |   return (master_th->th.th_teams_microtask && ap &&
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1457:15: warning: comparison between NULL and non-pointer ('kmp_va_list' (aka '__builtin_va_list') and NULL) [-Wnull-arithmetic]
 1457 |   return ((ap == NULL && active_level == 0) ||
      |            ~~ ^  ~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1457:15: error: invalid operands to binary expression ('kmp_va_list' (aka '__builtin_va_list') and 'long')
 1457 |   return ((ap == NULL && active_level == 0) ||
      |            ~~ ^  ~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1458:12: error: value of type 'kmp_va_list' (aka '__builtin_va_list') is not contextually convertible to 'bool'
 1458 |           (ap && teams_level > 0 && teams_level == level));
      |            ^~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1458:15: error: invalid operands to binary expression ('kmp_va_list' (aka '__builtin_va_list') and 'bool')
 1458 |           (ap && teams_level > 0 && teams_level == level));
      |            ~~ ^  ~~~~~~~~~~~~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1735:9: error: invalid argument type 'kmp_va_list' (aka '__builtin_va_list') to unary expression
 1735 |     if (!ap) {
      |         ^~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:2169:66: warning: comparison between NULL and non-pointer ('kmp_va_list' (aka '__builtin_va_list') and NULL) [-Wnull-arithmetic]
 2169 |             !(microtask == (microtask_t)__kmp_teams_master || ap == NULL))
      |                                                               ~~ ^  ~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:2169:66: error: invalid operands to binary expression ('kmp_va_list' (aka '__builtin_va_list') and 'long')
 2169 |             !(microtask == (microtask_t)__kmp_teams_master || ap == NULL))
      |                                                               ~~ ^  ~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:2284:9: error: value of type 'kmp_va_list' (aka '__builtin_va_list') is not contextually convertible to 'bool'
 2284 |     if (ap) {
      |         ^~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:2302:58: error: invalid argument type 'kmp_va_list' (aka '__builtin_va_list') to unary expression
 2302 |     __kmp_fork_team_threads(root, team, master_th, gtid, !ap);
      |                                                          ^~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:2363:9: error: value of type 'kmp_va_list' (aka '__builtin_va_list') is not contextually convertible to 'bool'
 2363 |     if (ap) {
      |         ^~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:7803:3: error: no matching function for call to '__kmp_fork_call'
 7803 |   __kmp_fork_call(loc, gtid, fork_context_intel, team->t.t_argc,
      |   ^~~~~~~~~~~~~~~
/home/brad/tmp/llvm-brad/openmp/runtime/src/kmp_runtime.cpp:1927:5: note: candidate function not viable: no known conversion from 'long' to 'kmp_va_list' (aka '__builtin_va_list') for 7th argument
 1927 | int __kmp_fork_call(ident_t *loc, int gtid,
      |     ^
 1928 |                     enum fork_context_e call_context, // Intel, GNU, ...
 1929 |                     kmp_int32 argc, microtask_t microtask, launch_t invoker,
 1930 |                     kmp_va_list ap) {
      |                     ~~~~~~~~~~~~~~
2 warnings and 11 errors generated.
```

openmp/runtime/src/kmp_os.h

@@ -219,7 +219,8 @@ typedef kmp_uint32 kmp_uint;
 
 // stdarg handling
 #if (KMP_ARCH_ARM || KMP_ARCH_X86_64 || KMP_ARCH_AARCH64 || KMP_ARCH_WASM) &&  \
-    (KMP_OS_FREEBSD || KMP_OS_LINUX || KMP_OS_WASI)
+    (KMP_OS_FREEBSD || KMP_OS_NETBSD || KMP_OS_OPENBSD || KMP_OS_DRAGONFLY ||  \
+     KMP_OS_LINUX || KMP_OS_WASI)
 typedef va_list *kmp_va_list;
 #define kmp_va_deref(ap) (*(ap))
 #define kmp_va_addr_of(ap) (&(ap))