[11u] RFR 8234535: Cross compilation fails due to missing CFLAGS for the BUILD_CC

[Christoph Göttschkes]

Hi,

please review this downport of JDK-8234535 to jdk11u-dev.

The changeset does not apply cleanly because of unrelated differences in 
the flags-cflags.m4 file surrounding the patch. Manually applying the 
patch was trivial.

Bug: https://bugs.openjdk.java.net/browse/JDK-8234535
Commit: https://hg.openjdk.java.net/jdk/jdk/rev/eef0bf57357c
Webrev: https://cr.openjdk.java.net/~cgo/8234535/webrev-11u.00/

Thanks,
Christoph