gardening: make c++98-compat-extra-semi an error

This cleans up 90 instances of this warning and reduces the build spew
when building on Linux.  This helps identify actual issues when
building which can get lost in the stream of warning messages.  It also
helps restore the ability to build the compiler with gcc.

lib/Serialization/SerializedModuleLoader.cpp

@@ -1468,7 +1468,7 @@ SerializedASTFile::getSourceOrderForDecl(const Decl *D) const {
 void SerializedASTFile::collectAllGroups(
     SmallVectorImpl<StringRef> &Names) const {
   File.collectAllGroups(Names);
-};
+}
 
 Optional<StringRef>
 SerializedASTFile::getGroupNameByUSR(StringRef USR) const {