Don't use __FUNCTION__ as a string literal

clang-cl doesn't support this and we don't gain much
from using it.
Merge branch 'master' of git://anongit.freedesktop.org/git/cairo
JOHNE - Modify the optimization for some of our Cairo sources

With these source modules fully optimized, Cairo wasn't properly rendering the small 'channel mute' buttons that we see in Ardour's Editor window (an empty black square was getting drawn where each button should be). Not really sure why... :-(