clover: Don't extend illegal integer types.

It's OK to pass them in memory, which is what kernel invocation needs.
Fixes regressions since llvm r337535 ("Reapply "AMDGPU: Fix handling of alignment padding in DAG argument lowering"):
	scalar-arithmetic-char
	scalar-arithmetic-uchar
	scalar-arithemtic-short
	scalar-arithmetic-ushort
	scalar-comparison-char
	scalar-comparison-uchar
	scalar-comparison-short
	scalar-comparison-ushort

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
(cherry picked from commit c2942141)
Merge conflicts resolved by Dylan

Conflicts:
	src/gallium/state_trackers/clover/llvm/compat.hpp