Move string utility functions into their own translation unit

hipify-clang/src/StringUtils.cpp

@@ -0,0 +1,17 @@
+#include "StringUtils.h"
+
+llvm::StringRef unquoteStr(llvm::StringRef s) {
+    if (s.size() > 1 && s.front() == '"' && s.back() == '"') {
+        return s.substr(1, s.size() - 2);
+    }
+
+    return s;
+}
+
+void removePrefixIfPresent(std::string &s, std::string prefix) {
+    if (s.find(prefix) != 0) {
+        return;
+    }
+
+    s.erase(0, prefix.size());
+}