mesa: bump required GCC version to 4.2.0
mesa: bump required GCC version to 4.2.0

It turns out Mesa hasn't compiled on less then 4.2 for a while
 so update conf to reflect this.

Signed-off-by: Timothy Arceri <7f85c8176b2576ffafd04ac63cd29ed35ff86cb6@yahoo.com.au>
Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler