[NFC][exegesis] SnippetGenerator::generateConfigurations(): don't forget to reserve()

Author: LebedevRI

llvm/tools/llvm-exegesis/lib/SnippetGenerator.cpp

@@ -75,6 +75,7 @@ Error SnippetGenerator::generateConfigurations(
       {
         BenchmarkCode BC;
         BC.Info = CT.Info;
+        BC.Key.Instructions.reserve(CT.Instructions.size());
         for (InstructionTemplate &IT : CT.Instructions) {
           if (auto error = randomizeUnsetVariables(State, ForbiddenRegs, IT))
             return error;