[libFuzzer] Disable Msan on InternalStrnlen

[vitalybuka]

Summary

It's called from ATTRIBUTE_NO_SANITIZE_MEMORY code.
It worked as expected if inlined and complained otherwise.

[eugenis]

LGTM

compiler-rt/lib/fuzzer/FuzzerTracePC.cpp

void TracePC::HandleCmp(uintptr_t PC, T Arg1, T Arg2) {
   else if (sizeof(T) == 8)
       TORC8.Insert(ArgXor, Arg1, Arg2);
   uint64_t HammingDistance = Popcountll(ArgXor);  // [0,64]
   uint64_t AbsoluteDistance = (Arg1 == Arg2 ? 0 : Clzll(Arg1 - Arg2) + 1);
   ValueProfileMap.AddValue(PC * 128 + HammingDistance);
   ValueProfileMap.AddValue(PC * 128 + 64 + AbsoluteDistance);
 }
 
+ATTRIBUTE_NO_SANITIZE_MEMORY
 static size_t InternalStrnlen(const char *S, size_t MaxLen) {
   size_t Len = 0;
   for (; Len < MaxLen && S[Len]; Len++) {}
   return Len;
 }
 
 // Finds min of (strlen(S1), strlen(S2)).
 // Needed because one of these strings may actually be non-zero terminated.
+ATTRIBUTE_NO_SANITIZE_MEMORY
 static size_t InternalStrnlen2(const char *S1, const char *S2) {
   size_t Len = 0;
   for (; S1[Len] && S2[Len]; Len++)  {}
   return Len;
 }
 
 void TracePC::ClearInlineCounters() {
   IterateCounterRegions([](const Module::Region &R){