[Flang/Flang-RT] Fix OldUnit tests on Windows (#150734)

Flang and Flang-RT have two flavours of unittests: 
1. GTest unittests, using lit's `lit.formats.GoogleTest` format ending
with `Tests${CMAKE_EXECUTABLE_SUFFIX}`
2. "non-GTest" or "OldUnit" unittests, a plain executable ending with
`.test${CMAKE_EXECUTABLE_SUFFIX}`

Both executables are emitted into the same unittests/ subdirectory. When
running ...
1. `tests/Unit/lit.cfg.py`, only considers executable ending with
`Tests` (or `Tests.exe` on Windows), hence skips the non-GTest tests.
2. `tests/NonGtestUnit/lit.cfg.py` considers all tests ending with
`.test` or `.exe`. On Windows, The GTest unitests also end with `.exe`.

In Flang-RT, `.exe` is considered an extension for non-GTest unitests
which causes tests such as Flang's `RuntimeTests.exe` to be executed for
both on Windows. This particular test includes a file write test, using
a hard-coded filename `ucsfile`. If the two instances are executed
concurrently, they might interfere with each other reading/writing
`ucsfile` which results in a flaky test.

This patch avoids the redundant execution by requiring the suffix
`.test.exe` on Windows. lit has to be modified because it uses
`os.path.splitext` the extract the extension, which would only recognize
the last component. It was changed from the orginal `endswith` in
c865abe747
for unknown reasons.

In Flang, `.exe` is not considered a suffix for non-GTest unittests and
hence they are not run at all. Fixing by also added `.test.exe` as valid
suffix, like with Flang-RT.

Unfortunately, the ` Evaluate/real.test.exe` test was failing on
Windows:
```
FAIL: flang-OldUnit :: Evaluate/real.test.exe (3592 of 3592)
******************** TEST 'flang-OldUnit :: Evaluate/real.test.exe' FAILED ********************
..\_src\flang\unittests\Evaluate\real.cpp:511: FAIL: FlagsToBits(prod.flags) == 0x18, not 0x10
        0 0x800001 * 0xbf7ffffe
..\_src\flang\unittests\Evaluate\real.cpp:511: FAIL: FlagsToBits(prod.flags) == 0x18, not 0x10
        0 0x800001 * 0x3f7ffffe
..\_src\flang\unittests\Evaluate\real.cpp:511: FAIL: FlagsToBits(prod.flags) == 0x18, not 0x10
        0 0x80800001 * 0xbf7ffffe
..\_src\flang\unittests\Evaluate\real.cpp:511: FAIL: FlagsToBits(prod.flags) == 0x18, not 0x10
        0 0x80800001 * 0x3f7ffffe
...
```
This is due to the `__x86_64__` macro not being set by Microsoft's
cl.exe and hence floating point status flags not being read out. The
equivalent macro for Microsofts compiler is `_M_X64` (or `_M_X64`).

flang-rt/test/NonGtestUnit/lit.cfg.py

@@ -8,8 +8,7 @@ import lit.formats
 config.name = "flang-rt-OldUnit"
 
 # suffixes: A list of file extensions to treat as test files.
-# On Windows, ".exe" also matches the GTests and will execited redundantly.
-config.suffixes = [".test", ".exe"]
+config.suffixes = [".test", ".test.exe"]
 
 # test_source_root: The root path where unit test binaries are located.
 config.test_source_root = os.path.join(config.flangrt_binary_dir, "unittests")

flang/include/flang/Common/target-rounding.h

@@ -21,7 +21,7 @@ struct Rounding {
   // (viz., fail to set the Underflow flag when an inexact product of a
   // multiplication is rounded up to a normal number from a subnormal
   // in some rounding modes)
-#if __x86_64__ || __riscv || __loongarch__
+#if __x86_64__ || _M_X64 || __riscv || __loongarch__
   bool x86CompatibleBehavior{true};
 #else
   bool x86CompatibleBehavior{false};

flang/include/flang/Testing/fp-testing.h

@@ -27,7 +27,7 @@ public:
 
 private:
   fenv_t originalFenv_;
-#if __x86_64__
+#if __x86_64__ || _M_X64
   unsigned int originalMxcsr;
 #endif
 };

flang/lib/Testing/fp-testing.cpp

@@ -11,7 +11,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
-#if __x86_64__
+#if __x86_64__ || _M_X64
 #include <xmmintrin.h>
 #endif
 
@@ -19,7 +19,7 @@ using Fortran::common::RealFlag;
 using Fortran::common::RoundingMode;
 
 ScopedHostFloatingPointEnvironment::ScopedHostFloatingPointEnvironment(
-#if __x86_64__
+#if __x86_64__ || _M_X64
     bool treatSubnormalOperandsAsZero, bool flushSubnormalResultsToZero
 #else
     bool, bool
@@ -38,7 +38,7 @@ ScopedHostFloatingPointEnvironment::ScopedHostFloatingPointEnvironment(
     std::abort();
   }
 
-#if __x86_64__
+#if __x86_64__ || _M_X64
   originalMxcsr = _mm_getcsr();
   unsigned int currentMxcsr{originalMxcsr};
   if (treatSubnormalOperandsAsZero) {
@@ -72,7 +72,7 @@ ScopedHostFloatingPointEnvironment::~ScopedHostFloatingPointEnvironment() {
         stderr, "fesetenv() failed: %s\n", llvm::sys::StrError(errno).c_str());
     std::abort();
   }
-#if __x86_64__
+#if __x86_64__ || _M_X64
   _mm_setcsr(originalMxcsr);
 #endif
 }

flang/test/NonGtestUnit/lit.cfg.py

@@ -4,7 +4,7 @@ import lit.Test
 
 config.name = "flang-OldUnit"
 
-config.suffixes = [".test"]
+config.suffixes = [".test", ".test.exe"]
 
 config.test_source_root = os.path.join(config.flang_obj_root, "unittests")
 config.test_exec_root = config.test_source_root

llvm/utils/lit/lit/formats/base.py

@@ -34,8 +34,7 @@ class FileBasedTest(TestFormat):
         if filename.startswith(".") or filename in localConfig.excludes:
             return
 
-        base, ext = os.path.splitext(filename)
-        if ext in localConfig.suffixes:
+        if any(filename.endswith(suffix) for suffix in localConfig.suffixes):
             yield lit.Test.Test(testSuite, path_in_suite, localConfig)
 
     def getTestsInDirectory(self, testSuite, path_in_suite, litConfig, localConfig):