Add option to not encode resource data into the C source file in order to embed the data using ld -b binary. This improves compilation times, but can only be done on Linux or other platforms with a supporting linker.

(Rebased by Philip Withnall, fixing minor rebase conflicts.)

Fixes #1489 (closed)

This is a rebase of !335 (closed) with some rebase conflicts fixed and a missing file listed in the gio/tests/Makefile.am.