[LSan] Parse common flags from LSAN_OPTIONS even if LSan is combined with
another sanitizer.

A user may run both LSan and LSan+ASan. It is weird to pass path to leak
suppression file (or other common sanitizer flags, like "verbosity") in
"LSAN_OPTIONS" in the first case and in "ASAN_OPTIONS" in the second case.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@215949 91177308-0d34-0410-b5e6-96231b3b80d8