[Support] Remove an unnecessary cast (NFC) (#146810)

We don't need to cast std::string to std::string.

Author: kazutakahirata

llvm/lib/Support/Signals.cpp

@@ -277,7 +277,7 @@ static bool printSymbolizedStackTrace(StringRef Argv0, void **StackTrace,
   // If we don't know argv0 or the address of main() at this point, try
   // to guess it anyway (it's possible on some platforms).
   std::string MainExecutableName =
-      sys::fs::exists(Argv0) ? (std::string)std::string(Argv0)
+      sys::fs::exists(Argv0) ? std::string(Argv0)
                              : sys::fs::getMainExecutable(nullptr, nullptr);
 
   auto SymbolizedAddressesOpt = collectAddressSymbols(