Fix -Wsign-compare warnings in parser, scanner, regexp, runtime.

src/regexp/regexp-parser.cc

Index: src/regexp/regexp-parser.cc
diff --git a/src/regexp/regexp-parser.cc b/src/regexp/regexp-parser.cc
index dba81ae9a712d616dc4f6a480bd45bf873e31db9..fd3123f674e3ca74986b945809cd7e439c09dc34 100644
--- a/src/regexp/regexp-parser.cc
+++ b/src/regexp/regexp-parser.cc
@@ -1607,7 +1607,7 @@ void RegExpBuilder::AddCharacter(uc16 c) {
 
 
 void RegExpBuilder::AddUnicodeCharacter(uc32 c) {
-  if (c > unibrow::Utf16::kMaxNonSurrogateCharCode) {
+  if (c > static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
     DCHECK(unicode());
     AddLeadSurrogate(unibrow::Utf16::LeadSurrogate(c));
     AddTrailSurrogate(unibrow::Utf16::TrailSurrogate(c));