Because the dynamic linker for 32-bit executables on 64-bit FreeBSD uses
the environment variable LD_32_LIBRARY_PATH instead of
LD_LIBRARY_PATH to find needed dynamic libraries, running the 32-bit
parts of the dynamic ASan tests will fail with errors similar to:
ld-elf32.so.1: Shared object "libclang_rt.asan-i386.so" not found, required by "Asan-i386-inline-Dynamic-Test"
This adds support for setting up LD_32_LIBRARY_PATH for the unit and
regression tests. It will likely also require a minor change to the
TestingConfig class in llvm/utils/lit/lit.