clover: Stub missing CL 1.2 functions.

clover: Stub missing CL 1.2 functions.

As sugested by Tom a long time ago
and in order to be able to create Piglit tests

v2:
replace NOT_SUPPORTED_BY_CL_1_1 macro with an inline function
remove extra space in clLinkProgram arg

v3:
use __func__

v4:
back to a macro, it make more sense to use it with __func__

[ Francisco Jerez: Rename to CLOVER_NOT_SUPPORTED_UNTIL and pass the
  minimum API version required by the entry point so the error
  messages don't become stale when support for additional CL versions
  is introduced. ]

Reviewed-by: Francisco Jerez <currojerez@riseup.net>