Fix compilation failure in test-macro-assembler[64].cc
caused by 8fcfe66f
due to warning `lambda-expression in unevaluated context`.

TEST=cctest/test-macro-assembler-mips[64]
BUG=

Review-Url: https://codereview.chromium.org/2543643005
Cr-Commit-Position: refs/heads/master@{#41433}