[ASTMatchers] Let registerMatcher() take a const char * instead of a StringRef

[mboehme]

Summary

r282433 added LLVM_ATTRIBUTE_ALWAYS_INLINE to the StringRef(const char *)
constructor. This causes the size of the stack frame for
RegistryMaps::RegistryMaps() to become excessive when compiling with gcc. This
change avoids inlining the StringRef constructor for every REGISTER_MATCHER
line.

[mboehme]

Abandoning after discussion with klimek.

lib/ASTMatchers/Dynamic/Registry.cpp

 class RegistryMaps {
 public:
   RegistryMaps();
   ~RegistryMaps();
 
   const ConstructorMap &constructors() const { return Constructors; }
 
 private:
-  void registerMatcher(StringRef MatcherName, MatcherDescriptor *Callback);
+  void registerMatcher(const char *MatcherName, MatcherDescriptor *Callback);
   ConstructorMap Constructors;
 };
 
-void RegistryMaps::registerMatcher(StringRef MatcherName,
+void RegistryMaps::registerMatcher(const char *MatcherName,
                                    MatcherDescriptor *Callback) {
   assert(Constructors.find(MatcherName) == Constructors.end());
   Constructors[MatcherName] = Callback;
 }
 
 #define REGISTER_MATCHER(name)                                                 \
   registerMatcher(#name, internal::makeMatcherAutoMarshall(                    \
                              ::clang::ast_matchers::name, #name));