meson: Fix reallocarray check

reallocarray() is defined in stdlib.h, so that would be right header to
check for its presense.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
(cherry picked from commit 5bb20fd3)
(cherry picked from commit 1d8cfe817861a0b0de2b561f6770e33d1242db63)