Libtest only support run in windows, so here add runtest_linux.sh for linux.

Issue： #I6V6HI
Test：cd third-party/musl/scripts && runtest_linux.sh
Signed-off-by: Nhhj <huanghuijin@huawei.com>
Change-Id: I0c5c78455f0e6d4a9e6e83d6e8f2c7f508e8c980