arb_compute_variable_group_size: Add argument to piglit_subtest functions.

arb_compute_variable_group_size: Add argument to piglit_subtest functions.

Fix Intel C++ Compiler warnings.

errors.c(223): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_variable_work_group_size_normal,
  		^

errors.c(229): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_variable_work_group_size_indirect,
  		^

errors.c(236): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_fixed_work_group_size,
  		^

errors.c(242): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_invalid_work_group_count_values,
  		^

errors.c(248): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_invalid_variable_work_group_size_values,
  		^

errors.c(254): warning #144: a value of type "enum piglit_result (*)()" cannot be used to initialize an entity of type "enum piglit_result (*)(void *)"
  		use_invalid_variable_group_invocations_values,
  		^

Fixes: ad38b44dd015 ("add ARB_compute_variable_group_size tests")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>