include: move ALLPERMS definition to compat.h

include: move ALLPERMS definition to compat.h

The Windows CI job started to fail as some libcephfs tests that use
ALLPERMS have been moved [1] to a separate file which doesn't have
the ALLPERMS definition.

  /ceph/src/test/libcephfs/suidsgid.cc:240:36: error: ‘ALLPERMS’ was
  not declared in this scope
  240 |   ASSERT_EQ(stx.stx_mode & (mode_t)ALLPERMS, before_mode);

We'll move this definition to compat.h so that we won't have to
redefine it in each file that uses it.

Note that we're moving the Windows "fs_compat.h" include up,
ensuring that the constants used by ALLPERMS are defined.

[1] https://github.com/ceph/ceph/commit/254eeb2730881ee48b4743e1422749d5b643f52a

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
(cherry picked from commit a2966c08171e006acfd9c32b00a1294f428c7e62)
Conflicts:
 - src/test/libcephfs/test.cc: with 'using namespace std'.