Add missing braces to bsearch inline implementation [BZ #28400]

GCC treats the pragma as a statement, so that the else branch only
consists of the pragma, not the return statement.

Fixes commit a725ff1d ("Suppress
-Wcast-qual warnings in bsearch").

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 32b96d0d)