clang build failing on Travis

The Travis clang builds are suddenly failing. Maybe the clang version was upgraded on Travis.

https://travis-ci.org/DynamoRIO/dynamorio/jobs/273692624

debug-internal-32: **** 4 build errors ****
	/.../dynamorio/suite/tests/linux/signal_racesys.c:104:28: error: implicit conversion from 'long long' to '__time_t' (aka 'long') changes value from 3155760000 to -1139207296 [-Werror,-Wconstant-conversion]
	make[2]: *** [suite/tests/CMakeFiles/linux.signal_racesys.dir/linux/signal_racesys.c.o] Error 1
	make[1]: *** [suite/tests/CMakeFiles/linux.signal_racesys.dir/all] Error 2
	make: *** [all] Error 2
release-external-32: **** 4 build errors ****
	CMake Error at /.../dynamorio/core/CMake_readelf.cmake:55 (message):
	make[2]: *** [lib32/release/libdynamorio.so] Error 1