Introduce qemu_madvise()

vl.c has a Sun-specific hack to supply a prototype for madvise(),
but the call site has apparently moved to arch_init.c.

Haiku doesn't implement madvise() in favor of posix_madvise().
OpenBSD and Solaris 10 don't implement posix_madvise() but madvise().
MinGW implements neither.

Check for madvise() and posix_madvise() in configure and supply qemu_madvise()
as wrapper. Prefer madvise() over posix_madvise() due to flag availability.
Convert all callers to use qemu_madvise() and QEMU_MADV_*.

Note that on Solaris the warning is fixed by moving the madvise() prototype,
not by qemu_madvise() itself. It helps with porting though, and it simplifies
most call sites.

v7 -> v8:
* Some versions of MinGW have no sys/mman.h header. Reported by Blue Swirl.

v6 -> v7:
* Adopt madvise() rather than posix_madvise() semantics for returning errors.
* Use EINVAL in place of ENOTSUP.

v5 -> v6:
* Replace two leftover instances of POSIX_MADV_NORMAL with QEMU_MADV_INVALID.
  Spotted by Blue Swirl.

v4 -> v5:
* Introduce QEMU_MADV_INVALID, suggested by Alexander Graf.
  Note that this relies on -1 not being a valid advice value.

v3 -> v4:
* Eliminate #ifdefs at qemu_advise() call sites. Requested by Blue Swirl.
  This will currently break the check in kvm-all.c by calling madvise() with
  a supported flag, which will not fail. Ideas/patches welcome.

v2 -> v3:
* Reuse the *_MADV_* defines for QEMU_MADV_*. Suggested by Alexander Graf.
* Add configure check for madvise(), too.
  Add defines to Makefile, not QEMU_CFLAGS.
  Convert all callers, untested. Suggested by Blue Swirl.
* Keep Solaris' madvise() prototype around. Pointed out by Alexander Graf.
* Display configure check results.

v1 -> v2:
* Don't rely on posix_madvise() availability, add qemu_madvise().
  Suggested by Blue Swirl.

Signed-off-by: Andreas Färber <afaerber@opensolaris.org>
Cc: Blue Swirl <blauwirbel@gmail.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>