[ELF2] Correctly set bits when -z now is specified.

The option now just sets NOW bit in DT_FLAGS_1 but some loaders
seem to require also BIND_NOW bit to be set in DT_FLAGS. This is,
also, what ld.bfd and gold do.

Differential Revision:	http://reviews.llvm.org/D13883

llvm-svn: 250799