folly: avoid false-positive ASAN-abort from SignalHandlerTest

Summary:
Without this change, the sig-handling test's deliberate
invalid access would trigger an ASAN-abort, which differed
from the expected SEGV.  Skip this test when ASAN is enabled.
* folly/experimental/symbolizer/test/SignalHandlerTest.cpp: Include
CPortability.h for definion of FOLLY_SANITIZE_ADDRESS.
(SignalHandler) [FOLLY_SANITIZE_ADDRESS]: Provide a different
regexp to match the first line of output from an ASAN-enabled binary.

Test Plan:
fbconfig --sanitize=address --platform-all=gcc-4.8.1-glibc-2.17 \
folly/experimental/symbolizer/test:signal_handler_test \
&& fbmake --fast runtests \
&& fbmake --fast runtests_opt

Sample output, before this change: https://phabricator.fb.com/P5428975
(search down to first AddressSanitizer abort.
With this change, expect that test to pass.

Reviewed By: lucian@fb.com

FB internal diff: D1164768