Implement command line options for stack probe space

This code adds the -mstack-probe-size command line option and implements the /Gs
compiler switch for clang-cl.

This should fix http://llvm.org/bugs/show_bug.cgi?id=21896

Patch by Andrew H!

Differential Revision: http://reviews.llvm.org/D6685

llvm-svn: 226601

clang/lib/Frontend/CompilerInvocation.cpp

@@ -523,6 +523,13 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
     Opts.StackAlignment = StackAlignment;
   }
 
+  if (Arg *A = Args.getLastArg(OPT_mstack_probe_size)) {
+    StringRef Val = A->getValue();
+    unsigned StackProbeSize = Opts.StackProbeSize;
+    Val.getAsInteger(0, StackProbeSize);
+    Opts.StackProbeSize = StackProbeSize;
+  }
+
   if (Arg *A = Args.getLastArg(OPT_fobjc_dispatch_method_EQ)) {
     StringRef Name = A->getValue();
     unsigned Method = llvm::StringSwitch<unsigned>(Name)