When testing on Linux/sparc64 with a `runtimes` build, the
`UBSan-Standalone-sparc :: TestCases/Misc/Linux/sigaction.cpp` test
`FAIL`s:
```
runtimes/runtimes-bins/compiler-rt/test/ubsan/Standalone-sparc/TestCases/Misc/Linux/Output/sigaction.cpp.tmp: error while loading shared libraries: libclang_rt.ubsan_standalone.so: wrong ELF class: ELFCLASS64
```
It turns out SPARC needs the same `LD_LIBRARY_PATH` handling as x86.
This is what this patch does, at the same time noticing that the current
duplication between `lit.common.cfg.py` and
`asan/Unit/lit.site.cfg.py.in` isn't necessary.
Tested on `sparc64-unknown-linux-gnu` and `x86_64-pc-linux-gnu`.
11903e8c96