oslib-posix: check for posix_memalign in configure script

Check for the presence of posix_memalign() in the configure script,
not using "defined(_POSIX_C_SOURCE) && !defined(__sun__)".  This
lets qemu use posix_memalign() on NetBSD versions that have it,
instead of falling back to valloc() which is wasteful when the
required alignment is smaller than a page.

Signed-off-by: Andreas Gustafsson <gson@gson.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

configure

@@ -4658,6 +4658,21 @@ if compile_prog "" "" ; then
     posix_madvise=yes
 fi
 
+##########################################
+# check if we have posix_memalign()
+
+posix_memalign=no
+cat > $TMPC << EOF
+#include <stdlib.h>
+int main(void) {
+    void *p;
+    return posix_memalign(&p, 8, 8);
+}
+EOF
+if compile_prog "" "" ; then
+    posix_memalign=yes
+fi
+
 ##########################################
 # check if we have posix_syslog
 
@@ -5746,6 +5761,7 @@ echo "preadv support    $preadv"
 echo "fdatasync         $fdatasync"
 echo "madvise           $madvise"
 echo "posix_madvise     $posix_madvise"
+echo "posix_memalign    $posix_memalign"
 echo "libcap-ng support $cap_ng"
 echo "vhost-net support $vhost_net"
 echo "vhost-scsi support $vhost_scsi"
@@ -6232,6 +6248,9 @@ fi
 if test "$posix_madvise" = "yes" ; then
   echo "CONFIG_POSIX_MADVISE=y" >> $config_host_mak
 fi
+if test "$posix_memalign" = "yes" ; then
+  echo "CONFIG_POSIX_MEMALIGN=y" >> $config_host_mak
+fi
 
 if test "$spice" = "yes" ; then
   echo "CONFIG_SPICE=y" >> $config_host_mak

util/oslib-posix.c

@@ -105,7 +105,7 @@ void *qemu_try_memalign(size_t alignment, size_t size)
         alignment = sizeof(void*);
     }
 
-#if defined(_POSIX_C_SOURCE) && !defined(__sun__)
+#if defined(CONFIG_POSIX_MEMALIGN)
     int ret;
     ret = posix_memalign(&ptr, alignment, size);
     if (ret != 0) {