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 master in 5 minutes and 32 seconds (queued for 1 second)
Status Job ID Name Coverage
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passed #89394
shared-build

00:05:32

passed #89395
static-build

00:04:27