Tests will timeout if they exceed time limit.

Default time limit is 5 minutes.

Override the default timeout of 5 minutes with LLDB_TEST_TIMEOUT.
LLDB_TEST_TIMEOUT=10m

Override the timeout for individual tests with LLDB_[TESTNAME]_TIMEOUT.
E.g., LLDB_TESTCONCURRENTEVENTS_TIMEOUT=2m

Set to "0" to run without timeout.

Submitted for Chaoren Lin

llvm-svn: 224171