desktop: -Werror=unused-macros

The documented feature test macro is _BSD_SOURCE, and anyway, feature
test macros must be defined before the first libc header is included, so
this one is evidently useless.

Change-Id: Ib4b2db0c6151c2f3df322992b189257f5dd0ea22
configure: let's default to GStreamer 1.0

Support was added 2 years ago, it is probably more likely to be
installed than 0.10 now.

Change-Id: Ia2e36725f50f96889eb602468840dde9259c2b90