gstreamer: drop manual CFLAGS

These were cargo-culted from MacPorts. The build system passes different
flags.
gstreamer: set env var instead of appending
gst-plugins-good: set env var instead of appending
enchant: make python an optional dependency.
bottle_version: support fontforge scheme.
hexchat: make python an optional dependency.
pyqwt: make python a hard dependency.
pyqwt: set PYTHONPATH in test.
vte: make python a hard dependency.
vte: add dependency on pygobject.
vte3: make python a hard dependency.
Don't assume cflags is non-nil

Fixes #29284.
mecab-ko 0.996-ko-0.9.1

Closes #29281.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
dcled 2.2
fontforge: make python an optional dependency.
libstfl: make python an optional dependency.
libtorrent-rasterbar: make python optional.
libxml2: make python an optional dependency.
llvm: make python an optional dependency.
postgres-xc: make python an optional dependency.