Remove clobber registers conflicting with input variables.

Remove clobber registers conflicting with input variables.

https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Clobbers specifies
that the clobber list should not overlap with the input or output.

Change-Id: I77fc2bfc6209ed325355193758f00fc171c8aebf
Reviewed-on: https://swiftshader-review.googlesource.com/8930
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>