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 <t_arceri@yahoo.com.au>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
1 file changed