[asan] Add basic support for Address Sanitizer function instrumentation

ASan allows to catch and diagnose memory corruption errors, which are possible
when using unsafe pointers.

This patch introduces a new driver/frontend option -sanitize=address to enable
ASan. When option is passed in, the ASan llvm passes will be turned on and
all functions will gain SanitizeAddress llvm attribute.

lib/Frontend/CompilerInvocation.cpp

@@ -15,6 +15,7 @@
 #include "swift/Strings.h"
 #include "swift/AST/DiagnosticsFrontend.h"
 #include "swift/Basic/Platform.h"
+#include "swift/Basic/SanitizerOptions.h"
 #include "swift/Option/Options.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Triple.h"
@@ -1224,6 +1225,10 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     }
   }
 
+  if (const Arg *A = Args.getLastArg(options::OPT_sanitize_EQ)) {
+    Opts.Sanitize = parseSanitizerArgValues(A, &Diags);;
+  }
+
   if (Args.hasArg(OPT_enable_reflection_metadata)) {
     Opts.StripReflectionMetadata = false;
     Opts.StripReflectionNames = false;