linux-user: Rename TARGET_ERESTARTSYS to QEMU_ERESTARTSYS

This value is fully internal to qemu, and so is not a TARGET define.
We use this as an extra marker for both host and target errno.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/xtensa/cpu_loop.c

@@ -184,7 +184,7 @@ void cpu_loop(CPUXtensaState *env)
                     env->regs[2] = ret;
                     break;
 
-                case -TARGET_ERESTARTSYS:
+                case -QEMU_ERESTARTSYS:
                     env->pc -= 3;
                     break;