[PATCH] configure.ac: Fix autoconf quoting breaking AC_FUNC_MEMCMP See the linked autoconf bug for details, but the gist is that AC_FUNC_MEMCMP ends up lacking the needed includes for string.h if a raw 'if' is used as opposed to AS_IF.
Quote properly with AS_IF to allow proper generation of the AC_FUNC_MEMCMP test and avoid -Wimplicit-function-declaration (which will be fatal in some compilers soon, like Clang 16) in its test.
Taken from: https://github.com/gentoo/gentoo/blob/c8feeb042d5c7725bc40f056a43467b0b50fb0b6/games-board/gnuchess/files/gnuchess-6.2.9-configure-quoting.patch
