Travis Mac build failing non-deterministically on decode test

The Travis Mac build suddenly failed in PR #4454. That error went away on a re-run. Then it happened again in PR #4455 :

https://travis-ci.com/github/DynamoRIO/dynamorio/jobs/392490440

====> FAILURE in debug-internal-64 <====
debug-internal-64: **** 4 build errors ****
	/.../dynamorio/build_debug-internal-64/suite/tests/decode.c_asm.asm:554: error: mismatch in operand sizes
	make[2]: *** [suite/tests/CMakeFiles/common.decode.dir/decode.c_asm.asm.o] Error 1
	make[1]: *** [suite/tests/CMakeFiles/common.decode.dir/all] Error 2
	make: *** [all] Error 2

The failure is unrelated to the PR's. It is strange that such a failure wouldn't be repeatable.