Fix the libgcc/libatomic link order.

The previous position of libgcc.a/libatomic.a on the link line causes
the linker to prefer satisfying dependencies from these libraries from
other libraries that might include them, rather than from libgcc.a (or
libatomic.a) itself. This imposes an ABI requirement that those
intermediate shared libraries _always_ export those symbols, which is
undesirable.

Change-Id: Ib593236b475d3e98356b2b1be6f96cee2b67378f