klee-uclibc detection is now a lot cleaner.

When building, a sym-link is created to klee-uclibc's libc.a file
in the same directory that the rest of KLEE's runtime libraries
are built.

When installing, klee-uclibc's libc.a file is installed in the same
directory that the rest of KLEE's runtime libraries are installed.

This essentially allows the correct location of klee-uclibc to
be found at runtime when KLEE is run from the build directory or
when it is installed.