libc: continue to use Android's custom linker script

By default, Android no longer compiles code using it's custom
linker script /build/core/armelf.xsc. However, this causes
problems for libc. Certain programs linked using older versions
of GOLD expect libc.so to export __exidx_start and __exidx_end.
Removing the custom linker script causes libc.so not to export
those symbols.

For now, continue using the old linker script, until we can
figure out a better solution.

Change-Id: Iaf002afd63a58b848818da24e5a4525620dc4d74