[LLVM][Cygwin] Enable conditions that are shared with MinGW

Cygwin and MinGW share the auto import behavior that could result in
__stack_check_guard being non-dso-local.  Allow windres to assume a
Cygwin target as well as a MinGW one, so defines like _WIN32 would not
be present on Cygwin.

Author: jeremyd2019

llvm/lib/CodeGen/TargetLoweringBase.cpp

@@ -2062,7 +2062,7 @@ void TargetLoweringBase::insertSSPDeclarations(Module &M) const {
 
     // FreeBSD has "__stack_chk_guard" defined externally on libc.so
     if (M.getDirectAccessExternalData() &&
-        !TM.getTargetTriple().isWindowsGNUEnvironment() &&
+        !TM.getTargetTriple().isOSCygMing() &&
         !(TM.getTargetTriple().isPPC64() &&
           TM.getTargetTriple().isOSFreeBSD()) &&
         (!TM.getTargetTriple().isOSDarwin() ||

llvm/tools/llvm-rc/llvm-rc.cpp

@@ -201,7 +201,7 @@ std::string getMingwTriple() {
   Triple T(sys::getDefaultTargetTriple());
   if (!isUsableArch(T.getArch()))
     T.setArch(getDefaultFallbackArch());
-  if (T.isWindowsGNUEnvironment())
+  if (T.isOSCygMing())
     return T.str();
   // Write out the literal form of the vendor/env here, instead of
   // constructing them with enum values (which end up with them in