mk: tests.mk simplify the method to clean arm testing directory
etc: modify adb_run_wrapper.sh to avoid 'expr' unrecognization at some android devices
etc: add TEST_EXEC_ENV for run-pass to adb_run_wrapper.sh
test: adjust some test cases for rpass on android
libstd: fix stat struct of android (SEGV error from run-pass/stat.rs on android)