qemu: fix building on mips arch

Add fallback zero value definition for MAP_SYNC etc. even when building
for CONFIG_LINUX.

Fixes openwrt/packages#11067

Reported-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

utils/qemu/patches/0006-util-mmap-alloc-fix-missing-MAP_SYNC.patch

@@ -0,0 +1,50 @@
+From f385b623c14b5208df88b0be479a9ab30ab68c72 Mon Sep 17 00:00:00 2001
+From: Yousong Zhou <yszhou4tech@gmail.com>
+Date: Mon, 30 Mar 2020 12:48:58 +0800
+Subject: [PATCH] util/mmap-alloc: fix missing MAP_SYNC
+
+Quote musl-libc commit 9b57db3f958 ("add MAP_SYNC and
+MAP_SHARED_VALIDATE from linux v4.15")
+
+ > for synchronous page faults, new in linux commit
+ > 1c9725974074a047f6080eecc62c50a8e840d050 and
+ > b6fb293f2497a9841d94f6b57bd2bb2cd222da43
+ > note that only targets that use asm-generic/mman.h have this new
+ > flag defined, so undef it on other targets (mips*, powerpc*).
+
+Fixes 119906afa5c ("util/mmap-alloc: support MAP_SYNC in
+qemu_ram_mmap()")
+
+Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
+---
+ util/mmap-alloc.c | 10 +++++++---
+ 1 file changed, 7 insertions(+), 3 deletions(-)
+
+diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
+index 27dcccd8ec..e133e38d21 100644
+--- a/util/mmap-alloc.c
++++ b/util/mmap-alloc.c
+@@ -12,9 +12,6 @@
+ 
+ #ifdef CONFIG_LINUX
+ #include <linux/mman.h>
+-#else  /* !CONFIG_LINUX */
+-#define MAP_SYNC              0x0
+-#define MAP_SHARED_VALIDATE   0x0
+ #endif /* CONFIG_LINUX */
+ 
+ #include "qemu/osdep.h"
+@@ -27,6 +24,13 @@
+ #include <sys/vfs.h>
+ #endif
+ 
++#ifndef MAP_SYNC
++#define MAP_SYNC              0x0
++#endif
++#ifndef MAP_SHARED_VALIDATE
++#define MAP_SHARED_VALIDATE   0x0
++#endif
++
+ size_t qemu_fd_getpagesize(int fd)
+ {
+ #ifdef CONFIG_LINUX