configure: add -Zhigh-mem linker flag for OS/2

When converting 1920x1080p mp4 using x264, x264 complains that it failed
to allocate memory. This flags makes it happy.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

configure.ac

@@ -279,7 +279,7 @@ case "${host_os}" in
     ;;
   *os2*)
     SYS=os2
-    LDFLAGS="${LDFLAGS} -Zomf -Zbin-files -Zargs-wild"
+    LDFLAGS="${LDFLAGS} -Zomf -Zbin-files -Zargs-wild -Zhigh-mem"
     ;;
   *)
     SYS="${host_os}"