This reverts d53cb6ffcf6fddc63c399fb2ea4620e682597b38. It emulated pre
glibc-2.2 behavior which was non-conforming.
The non-compliant behavior provoked https://reviews.llvm.org/D4418 which was intended to fix
-shared-libasan but introduced new problems (and caused some sanitizer tests to fail):
sanitizer interceptors were STB_GLOBAL instead of STB_WEAK, so defining
a second STB_GLOBAL interceptor can lead to a multiple definition linker error.
For example, in a
`-fsanitize={address,memory,...}` build, libc functions like
malloc/free/strtol/... cannot be provided by user object files.
See https://docs.freebsd.org/cgi/getmsg.cgi?fetch=16483939+0+archive/2014/freebsd-current/20140716.freebsd-current for discussions.