ANDROID: selftests: incfs: Add -fno-omit-frame-pointer

Without it incfs/incfs_perf runtime fails in format_signature:

malloc(): invalid size (unsorted)
Aborted

When compiled with gcc version 11.2.0.

Also add check for NULL after the malloc, and remove unneeded
space for uint32_t in signing_section.

Bug: 211066171

Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Change-Id: I62b775140e4b89f75335cbd65665cf6a3e0fe964