* ext/fileinfo/libmagic/file.h: delete HAVE_STRCASESTR ifdef

PHP's copy of libmagic doesn't use the strcasestr() function,
so there is no reason to prototype it, regardless of whether
or not the OS (libc) provides it.

* ext/fileinfo/libmagic.patch: update

Run ext/fileinfo/generate_patch.sh to re-roll this patch, a recent
commit removes HAVE_STRCASESTR from PHP's copy of libmagic.

* ext/fileinfo/config.{m4,w32}: don't compile strcasestr.c

Unlike the upstream library, PHP's copy of libmagic doesn't use the
strcasestr() function, so there is no reason to include strcasestr.c
in the list of source files.