ASSERT memval_simple "invalid size parameter"

Failures in the sample.memval_simple test on Fedora 27:

Release build: http://dynamorio.org/CDash/testDetails.php?test=518423&build=35316

ASSERT FAILURE: /work/dr/nightly/src/ext/drx/drx_buf.c:680: (0) ()

Debug build: http://dynamorio.org/CDash/testDetails.php?test=518361&build=35314

<Application /work/dr/nightly/run/build_debug-internal-64/suite/tests/bin/common.eflags (14583) DynamoRIO usage error : reg_32_to_opsz: invalid size parameter>
<Usage error: reg_32_to_opsz: invalid size parameter (/work/dr/nightly/src/core/arch/opnd_shared.c, line 2041)