[Basic] Update getSwiftRevision to return a StringRef

Author: xymus

include/swift/Basic/Version.h

@@ -181,7 +181,7 @@ std::string getSwiftFullVersion(Version effectiveLanguageVersion =
 
 /// Retrieves the repository revision number (or identifier) from which
 /// this Swift was built.
-std::string getSwiftRevision();
+StringRef getSwiftRevision();
 
 } // end namespace version
 } // end namespace swift

lib/Basic/Version.cpp

@@ -438,7 +438,7 @@ std::string getSwiftFullVersion(Version effectiveVersion) {
   return OS.str();
 }
 
-std::string getSwiftRevision() {
+StringRef getSwiftRevision() {
 #ifdef SWIFT_REVISION
   return SWIFT_REVISION;
 #else

lib/Serialization/ModuleFileSharedCore.cpp

@@ -325,7 +325,7 @@ validateControlBlock(llvm::BitstreamCursor &cursor,
 
       StringRef moduleRevision = blobData;
       if (isCompilerTagged && !moduleRevision.empty()) {
-        std::string compilerRevision = forcedDebugRevision ?
+        StringRef compilerRevision = forcedDebugRevision ?
           forcedDebugRevision : version::getSwiftRevision();
         if (moduleRevision != compilerRevision)
           result.status = Status::RevisionIncompatible;