Make latency test more consistent

Ensure the same value is used to set the latency and test the result

Author: r-belenov

llvm/unittests/tools/llvm-mca/X86/TestIncrementalMCA.cpp

@@ -245,7 +245,8 @@ TEST_F(X86TestBase, TestInstructionCustomization) {
                                 .addReg(X86::RAX);
   MCIs.push_back(InstructionToAdd);
   SmallVector<std::pair<StringRef, StringRef>> InstrDescs;
-  InstrDescs.push_back(std::make_pair(StringRef("LATENCY"), StringRef("100")));
+  auto LatStr = std::to_string(ExplicitLatency);
+  InstrDescs.push_back(std::make_pair(StringRef("LATENCY"), StringRef(LatStr)));
 
   // Run the baseline.
   json::Object BaselineResult;