linux-user: Define TARGET_QEMU_ESIGRETURN for mipsn32

Copied from mips/syscall.h.
Signed-off-by: NUlrich Hecht <uli@suse.de>
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/mipsn32/syscall.h

@@ -218,4 +218,7 @@ struct target_pt_regs {
 
 
 
+/* Nasty hack: define a fake errno value for use by sigreturn. */
+#define TARGET_QEMU_ESIGRETURN 255
+
 #define UNAME_MACHINE "mips64"