clover: Move back to using build_error to signal compilation failure.

clover: Move back to using build_error to signal compilation failure.

This partially reverts 7e0180d57d330bd8d3047e841086712376b2a1cc.
Having two different exception subclasses for compilation and linking
makes it more difficult to share or move code between the two
codepaths, because the exact same function under the same error
condition would need to throw one exception or the other depending on
what top-level API is being implemented with it.  There is little
benefit anyway because clCompileProgram() and clLinkProgram() can tell
whether they are linking or compiling a program.

Reviewed-by: Serge Martin <edb+mesa@sigluy.net>
Tested-by: Jan Vesely <jan.vesely@rutgers.edu>