maintainer-feedback requested: [Bug 279367] java/openjdk11 -- build with the base compiler, not custom LLVM

Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-java (Nobody)
<java@FreeBSD.org> for maintainer-feedback:
Bug 279367: java/openjdk11 -- build with the base compiler, not custom LLVM
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=279367



--- Description ---
It is somewhat disheartening, how easily port-maintainers give up upon
encountering problems with the base compiler -- and make a custom compiler a
requirement instead...

openjdk11 currently requires an LLVM -- of version 12 -- and this PR seeks to
fix that.

The proposal adds a patch, which was once part of the opendjk17 port back in
(see Bug 274109). This fixes the problem with the linking.

Separately, the now-fatal compiler warning is explicitly disabled -- so the
code compiles.

It also places the custom CFLAGS, CXXFLAGS, and LDFLAGS into the CONFIGURE_ARGS
(as the JDK maintainers want).