[Clang][Cygwin] Enable few conditions that are shared with MinGW

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -1953,7 +1953,7 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
           // silently there. For other targets that have ms_struct enabled
           // (most probably via a pragma or attribute), trigger a diagnostic
           // that defaults to an error.
-          if (!Context.getTargetInfo().getTriple().isWindowsGNUEnvironment())
+          if (!Context.getTargetInfo().getTriple().isOSCygMing())
             Diag(D->getLocation(), diag::warn_npot_ms_struct);
         }
         if (TypeSize > FieldAlign &&

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -1530,10 +1530,10 @@ static bool shouldAssumeDSOLocal(const CIRGenModule &cgm,
 
   const llvm::Triple &tt = cgm.getTriple();
   const CodeGenOptions &cgOpts = cgm.getCodeGenOpts();
-  if (tt.isWindowsGNUEnvironment()) {
-    // In MinGW, variables without DLLImport can still be automatically
-    // imported from a DLL by the linker; don't mark variables that
-    // potentially could come from another DLL as DSO local.
+  if (tt.isOSCygMing()) {
+    // In MinGW and Cygwin, variables without DLLImport can still be
+    // automatically imported from a DLL by the linker; don't mark variables
+    // that potentially could come from another DLL as DSO local.
 
     // With EmulatedTLS, TLS variables can be autoimported from other DLLs
     // (and this actually happens in the public interface of libstdc++), so

clang/lib/Driver/ToolChain.cpp

@@ -773,7 +773,7 @@ std::string ToolChain::buildCompilerRTBasename(const llvm::opt::ArgList &Args,
     break;
   case ToolChain::FT_Shared:
     if (TT.isOSWindows())
-      Suffix = TT.isWindowsGNUEnvironment() ? ".dll.a" : ".lib";
+      Suffix = TT.isOSCygMing() ? ".dll.a" : ".lib";
     else if (TT.isOSAIX())
       Suffix = ".a";
     else

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5965,7 +5965,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-mms-bitfields");
   }
 
-  if (Triple.isWindowsGNUEnvironment()) {
+  if (Triple.isOSCygMing()) {
     Args.addOptOutFlag(CmdArgs, options::OPT_fauto_import,
                        options::OPT_fno_auto_import);
   }

clang/lib/Frontend/InitPreprocessor.cpp

@@ -945,8 +945,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   if (LangOpts.GNUCVersion && LangOpts.CPlusPlus11)
     Builder.defineMacro("__GXX_EXPERIMENTAL_CXX0X__");
 
-  if (TI.getTriple().isWindowsGNUEnvironment()) {
-    // Set ABI defining macros for libstdc++ for MinGW, where the
+  if (TI.getTriple().isOSCygMing()) {
+    // Set ABI defining macros for libstdc++ for MinGW and Cygwin, where the
     // default in libstdc++ differs from the defaults for this target.
     Builder.defineMacro("__GXX_TYPEINFO_EQUALITY_INLINE", "0");
   }

clang/lib/Sema/SemaDecl.cpp

@@ -12578,9 +12578,9 @@ static bool isDefaultStdCall(FunctionDecl *FD, Sema &S) {
   if (FD->getName() == "main" || FD->getName() == "wmain")
     return false;
 
-  // Default calling convention for MinGW is __cdecl
+  // Default calling convention for MinGW and Cygwin is __cdecl
   const llvm::Triple &T = S.Context.getTargetInfo().getTriple();
-  if (T.isWindowsGNUEnvironment())
+  if (T.isOSCygMing())
     return false;
 
   // Default calling convention for WinMain, wWinMain and DllMain