linux-user: Do not report "Unsupported syscall" by default

This can still be reported using the "-d unimp" command line option.

Fixes: https://bugs.launchpad.net/qemu/+bug/1777226Reported-by: NJohn Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Suggested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <20180706155127.7483-2-f4bug@amsat.org>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

linux-user/syscall.c

@@ -12757,7 +12757,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 
     default:
     unimplemented:
-        gemu_log("qemu: Unsupported syscall: %d\n", num);
+        qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
 #if defined(TARGET_NR_setxattr) || defined(TARGET_NR_get_thread_area) || defined(TARGET_NR_getdomainname) || defined(TARGET_NR_set_robust_list)
     unimplemented_nowarn:
 #endif