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/riscv/cpu_loop.c

@@ -69,7 +69,7 @@ void cpu_loop(CPURISCVState *env)
                                  env->gpr[xA5],
                                  0, 0);
             }
-            if (ret == -TARGET_ERESTARTSYS) {
+            if (ret == -QEMU_ERESTARTSYS) {
                 env->pc -= 4;
             } else if (ret != -TARGET_QEMU_ESIGRETURN) {
                 env->gpr[xA0] = ret;