work around _FORTIFY_SOURCE false positive

In builds with profiling disabled (default), the opt_prof_prefix array
has a one byte length as a micro-optimization. This will cause the usage
of write in the unused profiling code to be statically detected as a
buffer overflow by Bionic's _FORTIFY_SOURCE implementation as it tries
to detect read overflows in addition to write overflows.

This works around the problem by informing the compiler that
not_reached() means code in unreachable in release builds.

(cherry picked from commit 67c46a9e5366b3461d9f1e733129c792628c337b)

Change-Id: I8c156bfd0751a19d6abb60e503169c6461d23175
1 file changed