Revert "standalone-examples: support custom GCC lib"

After further testing, this patch has two problems.  First,
examples/standalone/Makefile was already inherting PLATFORM_LIBS from
the top-level Makefile so this lead to duplicating the private libgcc.
Second, currently the private libgcc has a reference to 'hang' that is
not being fulfilled.

This reverts commit 4412db46.

Signed-off-by: Tom Rini <trini@ti.com>