Compiling C and C++ files together using GCC

I'm trying to compile C and C++ sources together using GCC.

gcc -std=c++0x test.cpp -std=c99 test.c -lstdc++

Now, this works fine, except that I get two warnings.

cc1plus: warning: command line option "-std=c99" is valid for C/ObjC but not for C++
cc1: warning: command line option "-std=c++0x" is valid for C++/ObjC++ but not for C

Therefore I can't use -Werror with this setup. Can these warnings be suppressed somehow?