Fix --enable-checking build with macOS clang 15.0.0

Fix --enable-checking build with macOS clang 15.0.0

search.c:3428:7: error: call to undeclared library function 'free' ...

configure:9131: checking for C compiler version
configure:9140: gcc --version >&5
Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: arm64-apple-darwin23.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

* src/search.c: Include stdlib.h for free(), and stdio.h for
open_memstream(), fclose().

Copyright-paperwork-exempt: yes
(cherry picked from commit 3ea451042a34a44da94176f27ea354e6823e68ee)