Steven Newbury has pointed out to me that the way we're changing install location for clang breaks multilib system with SYMLINK_LIB=no.
Since clang is multitarget, the lib/clang contains both 64-bit and 32-bit resources. Moving that to $(get_libdir) is wrong, and clang fails to find the system headers.
The suggested fix is to drop the libdir substitution completely. I will test it later today when I get near distcc.
I think this is fixed since 3.3-r3 or so.