clang-cl: support __cdecl-on-struct anachronism

Summary:
The Microsoft compiler emits

  warning C4229: anachronism used : modifiers on data are ignored

for

  struct {} __cdecl s;

but ICU's gendict can generate such (and does when building
LibreOffice), so accepting this in clang-cl too would be useful.

Reviewers: rnk

Patch by Stephan Bergmann

Differential Revision: http://reviews.llvm.org/D16628

llvm-svn: 263947

clang/lib/Parse/ParseDeclCXX.cpp

@@ -1103,6 +1103,15 @@ bool Parser::isValidAfterTypeSpecifier(bool CouldBeBitfield) {
     return true;
   case tok::colon:
     return CouldBeBitfield;     // enum E { ... }   :         2;
+  // Microsoft compatibility
+  case tok::kw___cdecl:         // struct foo {...} __cdecl      x;
+  case tok::kw___fastcall:      // struct foo {...} __fastcall   x;
+  case tok::kw___stdcall:       // struct foo {...} __stdcall    x;
+  case tok::kw___thiscall:      // struct foo {...} __thiscall   x;
+  case tok::kw___vectorcall:    // struct foo {...} __vectorcall x;
+    // We will diagnose these calling-convention specifiers on non-function
+    // declarations later, so claim they are valid after a type specifier.
+    return getLangOpts().MicrosoftExt;
   // Type qualifiers
   case tok::kw_const:           // struct foo {...} const     x;
   case tok::kw_volatile:        // struct foo {...} volatile  x;

clang/test/Parser/ms-anachronism.c

@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -triple i686-windows-msvc -fms-extensions -fsyntax-only -verify %s
+
+struct {} __cdecl s; // expected-warning {{'__cdecl' only applies to function types; type here is 'struct}}