Two changes:

1. Get rid of TOOLLINKOPTS as it is a hold over from llvm-test and only
   used to communicate additional libraries to the linker. The *standard*
   way to do that is with the LIBS variable which this change supports.

2. Allow the TARGETS_TO_BUILD variable to be set from the configuration
   substitution. This is the result of the --enable-target= parameter to
   the configure script.

llvm-svn: 21449