[llvm-exegesis] Use const reference for range variable

In the SubprocessMemory destructor, I was using a normal std::string to
hold the name of the current shared memory name, but a const reference
works just as well in this situation while having better performance
characteristics.

Fixes llvm#90289

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

@@ -143,7 +143,7 @@ Expected<int> SubprocessMemory::setupAuxiliaryMemoryInSubprocess(
 }
 
 SubprocessMemory::~SubprocessMemory() {
-  for (std::string SharedMemoryName : SharedMemoryNames) {
+  for (const std::string &SharedMemoryName : SharedMemoryNames) {
     if (shm_unlink(SharedMemoryName.c_str()) != 0) {
       errs() << "Failed to unlink shared memory section: " << strerror(errno)
              << "\n";