[Clang][Cygwin] Enable few conditions that are shared with MinGW (llvm#149637)

The Cygwin target is generally very similar to the MinGW target. The
default auto-import behavior, the default calling convention, the
`.dll.a` import library extension, the `__GXX_TYPEINFO_EQUALITY_INLINE`
pre-define by `g++`, and the long double configuration.

Co-authored-by: Mateusz Mikuła <[email protected]>

Author: jeremyd2019

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -1946,7 +1946,7 @@ 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/Driver/ToolChain.cpp

@@ -749,7 +749,7 @@ std::string ToolChain::buildCompilerRTBasename(const llvm::opt::ArgList &Args,
     break;
   case ToolChain::FT_Shared:
     Suffix = TT.isOSWindows()
-                 ? (TT.isWindowsGNUEnvironment() ? ".dll.a" : ".lib")
+                 ? (TT.isOSCygMing() ? ".dll.a" : ".lib")
                  : ".so";
     break;
   }

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6121,7 +6121,7 @@ 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

@@ -12514,9 +12514,9 @@ 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

clang/test/CodeGen/ms_struct-long-double.c

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -emit-llvm-only -triple i686-windows-gnu -fdump-record-layouts %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm-only -triple i686-windows-cygnus -fdump-record-layouts %s | FileCheck %s
 // RUN: %clang_cc1 -emit-llvm-only -triple i686-linux -fdump-record-layouts -Wno-incompatible-ms-struct %s | FileCheck %s
 // RUN: not %clang_cc1 -emit-llvm-only -triple i686-linux -fdump-record-layouts %s 2>&1 | FileCheck %s -check-prefix=ERROR
 

clang/test/Preprocessor/Inputs/llvm-windres.h

@@ -1,10 +1,12 @@
 #ifndef RC_INVOKED
-#error RC_INVOKED not defined
+#  error RC_INVOKED not defined
 #endif
-#ifndef _WIN32
-#error _WIN32 not defined
-#endif
-#ifndef __MINGW32__
-#error __MINGW32__ not defined
+#ifndef __CYGWIN__
+#  ifndef _WIN32
+#    error _WIN32 not defined
+#  endif
+#  ifndef __MINGW32__
+#    error __MINGW32__ not defined
+#  endif
 #endif
 #define MY_ID 42