fixup! Add test for gcc_struct

Author: DanShaders

clang/lib/AST/Decl.cpp

@@ -5125,10 +5125,10 @@ void RecordDecl::completeDefinition() {
 /// This which can be turned on with an attribute, pragma, or the
 /// -mms-bitfields command-line option.
 bool RecordDecl::isMsStruct(const ASTContext &C) const {
-  if (hasAttr<MSStructAttr>())
-    return true;
   if (hasAttr<GCCStructAttr>())
     return false;
+  if (hasAttr<MSStructAttr>())
+    return true;
   auto LayoutCompatibility = C.getLangOpts().getLayoutCompatibility();
   if (LayoutCompatibility == LangOptions::LayoutCompatibilityKind::Default)
     return C.defaultsToMsStruct();

clang/test/CodeGen/gcc_struct.c

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-pc-linux-gnu %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-pc-linux-gnu -fms-layout-compatibility=microsoft %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-pc-windows-gnu %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-pc-windows-gnu -fms-layout-compatibility=itanium %s
+
+struct {
+    int a : 24;
+    char b : 8;
+} __attribute__((gcc_struct)) t1;
+static int a1[(sizeof(t1) == 4) - 1];
+
+#pragma ms_struct on
+struct {
+    int a : 24;
+    char b : 8;
+} __attribute__((gcc_struct)) t2;
+static int a2[(sizeof(t2) == 4) - 1];
+#pragma ms_struct off