libgphoto2: builds failing on some buildbots

[mascguy (Christopher Nielsen)]

This port is still failing to build on some of our buildbots:

​https://ports.macports.org/port/libgphoto2/builds/

I'm also seeing similar local build failures, on macOS 10.12 through 10.14.

The compilation error appears (?) to be related to source file pentax/js0n.c:

libtool: compile:  /usr/bin/clang -DHAVE_CONFIG_H -I. -I.. -D_GPHOTO2_INTERNAL_CODE -DLOCALEDIR=\"/opt/local/share/locale\" -DCAMLIBS=\"/opt/local/lib/libgphoto2/2.5.28\" -I.. -I.. -I../libgphoto2_port -I/opt/local/include -Wno-unused -pipe -Os -arch x86_64 -Werror=unknown-warning-option -Wall -Wextra -Weverything -Wno-error=documentation-deprecated-sync -Wno-unused-parameter -DLIBGPHOTO2 -DPKTDATADIR=\"/\" -pipe -Os -arch x86_64 -Werror=unknown-warning-option -Wall -Wextra -Weverything -Wno-error=documentation-deprecated-sync -Wno-unused-parameter -MT pentax/la-js0n.lo -MD -MP -MF pentax/.deps/la-js0n.Tpo -c pentax/js0n.c  -fno-common -DPIC -o pentax/.libs/la-js0n.o

pentax/js0n.c:14:32: error: unknown warning group '-Woverride-init', ignored [-Werror,-Wunknown-warning-option]

Blacklisting Clang versions prior to 1001 fixes the issue locally, though that's not ideal.

The best approach might be to simply eliminate the use of compiler option -Werror=unknown-warning-option. But I haven't had a chance to test that theory, and it's unclear whether that's the only issue.

Alternatively, perhaps this might come down to the declared compiler standard needed? (That's a bit of a stretch, though.)

But all of the above is speculation, as I haven't had much time to dig into this.