clover: Add clLinkProgram (CL 1.2).
clover: Add clLinkProgram (CL 1.2).

[ Francisco Jerez: Use validate_build_common for error checking,
  simplify control flow slightly and handle additional exception
  types. ]

Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>
Tested-by: Jan Vesely <ed664c4bb5cadd95cb7521d1190a56e280fa6954@rutgers.edu>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler