ports r430424 broke the build on armv6.
USE_PRECOMPILED_HEADER is set to 0 now on armv6 and it shouldn't. The logic was reversed here: https://svnweb.freebsd.org/ports/head/java/openjdk8/Makefile?revision=432697&view=markup#l368
A commit references this bug:
Date: Thu Feb 2 21:28:22 UTC 2017
New revision: 433180
Fix build with GCC. It was broken by r430424.