[tools] Unbreak the GCC build (workaround a GCC bug).

../tools/llvm-extract/llvm-extract.cpp: In function ‘int main(int, char**)’:
warning: ISO C++ forbids zero-size array ‘argv’ [-Wpedantic]

GCC reference bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61259

llvm-svn: 286396

llvm/tools/llvm-extract/llvm-extract.cpp

@@ -223,7 +223,8 @@ int main(int argc, char **argv) {
     }
   }
 
-  ExitOnError ExitOnErr(std::string(argv[0]) + ": error reading input: ");
+  // Use *argv instead of argv[0] to work around a wrong GCC warning.
+  ExitOnError ExitOnErr(std::string(*argv) + ": error reading input: ");
 
   auto Materialize = [&](GlobalValue &GV) { ExitOnErr(GV.materialize()); };