[Clang] [Driver] use __cxa_atexit by default on Cygwin. (llvm#135701)

GCC on Cygwin and MSYS2 are built with --enable-__cxa_atexit.

Adjust test to expect this change.

Author: jeremyd2019

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7230,7 +7230,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // -fuse-cxa-atexit is default.
   if (!Args.hasFlag(
           options::OPT_fuse_cxa_atexit, options::OPT_fno_use_cxa_atexit,
-          !RawTriple.isOSAIX() && !RawTriple.isOSWindows() &&
+          !RawTriple.isOSAIX() &&
+              (!RawTriple.isOSWindows() ||
+               RawTriple.isWindowsCygwinEnvironment()) &&
               ((RawTriple.getVendor() != llvm::Triple::MipsTechnologies) ||
                RawTriple.hasEnvironment())) ||
       KernelOrKext)

clang/test/Driver/cxa-atexit.cpp

@@ -1,15 +1,15 @@
 // RUN: %clang -### -target armv7-unknown-windows-msvc -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target armv7-unknown-windows-itanium -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target armv7-unknown-windows-gnu -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
-// RUN: %clang -### -target armv7-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
+// RUN: %clang -### -target armv7-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-CYGWIN
 // RUN: %clang -### -target i686-unknown-windows-msvc -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target i686-unknown-windows-itanium -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target i686-unknown-windows-gnu -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
-// RUN: %clang -### -target i686-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
+// RUN: %clang -### -target i686-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-CYGWIN
 // RUN: %clang -### -target x86_64-unknown-windows-msvc -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target x86_64-unknown-windows-itanium -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
 // RUN: %clang -### -target x86_64-unknown-windows-gnu -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
-// RUN: %clang -### -target x86_64-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-WINDOWS
+// RUN: %clang -### -target x86_64-unknown-windows-cygnus -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-CYGWIN
 // RUN: %clang -### -target hexagon-unknown-none -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-HEXAGON
 // RUN: %clang -### -target xcore-unknown-none -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-XCORE
 // RUN: %clang -### -target armv7-mti-none -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-MTI
@@ -21,6 +21,7 @@
 // RUN: %clang -### -target powerpc64-ibm-aix-xcoff -c %s -o /dev/null 2>&1 | FileCheck %s -check-prefix CHECK-AIX
 
 // CHECK-WINDOWS: "-fno-use-cxa-atexit"
+// CHECK-CYGWIN-NOT: "-fno-use-cxa-atexit"
 // CHECK-SOLARIS-NOT: "-fno-use-cxa-atexit"
 // CHECK-HEXAGON-NOT: "-fno-use-cxa-atexit"
 // CHECK-XCORE: "-fno-use-cxa-atexit"