Teach LLVM-Config to use logical target names (1/2)

LLVM library names are now available as logical CMake targets both
to our own build and to application CMake code.  Replace use of
'list(FIND)' with a simple 'if(TARGET)' to determine whether a
library is available.

Contributed by Brad King.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201852 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed