src/fccache.c: Fix define for HAVE_POSIX_FADVISE

Otherwise, there would be build errors in the following 2 cases:
* define HAVE_POSIX_FADVISE
Or:
* undef HAVE_POSIX_FADVISE

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
2 jobs for fadvise-fix in 5 minutes and 6 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #89392
shared-build

00:05:06

passed #89393
static-build

00:04:43