Silence the driver warnings, if we see "-w" on the Driver.

[filcab]

Summary

This patch is basically a request for comments. Since we can enable
warnings after that -w, I don't think the patch is 100% correct.

The problem that triggered this is because we have some amount of tests
that expect 0 warnings (including unit tests for -w), but -w ends up not
fully silencing everything.

[chandlerc]

LGTM

cfe/trunk/lib/Driver/Driver.cpp

Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
 
   // FIXME: What are we going to do with -V and -b?
 
   // FIXME: This stuff needs to go into the Compilation, not the driver.
   bool CCCPrintPhases;
 
   InputArgList Args = ParseArgStrings(ArgList.slice(1));
 
+  // Silence driver warnings if requested
+  Diags.setIgnoreAllWarnings(Args.hasArg(options::OPT_w));
+
   // -no-canonical-prefixes is used very early in main.
   Args.ClaimAllArgs(options::OPT_no_canonical_prefixes);
 
   // Ignore -pipe.
   Args.ClaimAllArgs(options::OPT_pipe);
 
   // Extract -ccc args.
   //

cfe/trunk/test/Index/warning-flags.c

 int foo() { }
 int *bar(float *f) { return f; }
 
 // RUN: c-index-test -test-load-source all %s 2>&1|FileCheck -check-prefix=CHECK-BOTH-WARNINGS %s
 // RUN: c-index-test -test-load-source-reparse 5 all %s 2>&1|FileCheck -check-prefix=CHECK-BOTH-WARNINGS %s
 // RUN: c-index-test -test-load-source all -Wno-return-type  %s 2>&1|FileCheck -check-prefix=CHECK-SECOND-WARNING %s
 // RUN: c-index-test -test-load-source-reparse 5 all -Wno-return-type %s 2>&1|FileCheck -check-prefix=CHECK-SECOND-WARNING %s
 // RUN: c-index-test -test-load-source all -w %s 2>&1|not grep warning:
 // RUN: c-index-test -test-load-source-reparse 5 all -w %s 2>&1|not grep warning:
+// RUN: c-index-test -test-load-source all -w -O4 %s 2>&1|not grep warning:
 
 // CHECK-BOTH-WARNINGS: warning: control reaches end of non-void function
 // CHECK-BOTH-WARNINGS: warning: incompatible pointer types returning 'float *' from a function with result type 'int *'
 
 // CHECK-SECOND-WARNING-NOT:control reaches end of non-void
 // CHECK-SECOND-WARNING: warning: incompatible pointer types returning 'float *' from a function with result type 'int *'