Implemented correct stack probing on mingw/cygwin for dynamic alloca's.
Also, fixed static case in presence of eax livin. This fixes PR331

PS: Why don't we still have push/pop instructions? :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36195 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/CBackend/CBackend.cpp b/lib/Target/CBackend/CBackend.cpp
index 83704a3..ac7251f 100644
--- a/lib/Target/CBackend/CBackend.cpp
+++ b/lib/Target/CBackend/CBackend.cpp
@@ -1281,8 +1281,8 @@
   // Alloca is hard to get, and we don't want to include stdlib.h here.
   Out << "/* get a declaration for alloca */\n"
       << "#if defined(__CYGWIN__) || defined(__MINGW32__)\n"
-      << "extern void *_alloca(unsigned long);\n"
-      << "#define alloca(x) _alloca(x)\n"
+      << "#define  alloca(x) __builtin_alloca((x))\n"
+      << "#define _alloca(x) __builtin_alloca((x))\n"    
       << "#elif defined(__APPLE__)\n"
       << "extern void *__builtin_alloca(unsigned long);\n"
       << "#define alloca(x) __builtin_alloca(x)\n"