[runtime] Port simple String.prototype.indexOf cases to TF Builtin

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index e1fb9b0a5ec6c66a57c85c5e63c3a7bc88b0b150..5b4613ee48ea05dec1aa4d8e0efe4eaab436cb18 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -1029,6 +1029,8 @@ class ExternalReference BASE_EMBEDDED {
   static ExternalReference ieee754_tan_function(Isolate* isolate);
   static ExternalReference ieee754_tanh_function(Isolate* isolate);
 
+  static ExternalReference libc_memchr_function(Isolate* isolate);
+
   static ExternalReference page_flags(Page* page);
 
   static ExternalReference ForDeoptEntry(Address entry);
@@ -1117,6 +1119,7 @@ V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostream&, ExternalReference);
 
 // -----------------------------------------------------------------------------
 // Utility functions
+void* libc_memchr(void* string, int character, size_t search_length);
 
 inline int NumberOfBitsSet(uint32_t x) {
   unsigned int num_bits_set;