Put shared library ldflags first

Some obscure modules (like libtest_with_dependency_loop_b_tmp in
bionic/tests/libs/Android.bp) need to override shared library flags like
-Wl,-soname.  Put the defaults first so that the module specific ones
can override them.

Change-Id: Icde9ca2cf76c4f3e3218b6b22033bc81a6755b57