gitignore: negate gitignore for static pkgconfig files

Commit 781f253 adds a rule cairo-*.*.* to .gitignore in the root dir.
Unfortunately this matches several src/cairo-*.pc.in files in the
src directory.

The build system requires these files to be present, but the rule is
allowing them to be ignored. For example, when extracting a cgit
snapshot tarball and checking it into another git repository, these
files get left behind. Any accidental changes to these files will go
unnoticed by a 'git status' (possibly creating bad installs) and
any intentional changes could not be committed (git commit -a will
miss them, and every one will need to be forced). This is not really
desirable.

We don't want to unignore *.pc.in here since there are many, many
autogenerated files with this name, and the cairo-*.*.* rule is in
general quite useful and doesn't warrant modification (although it
could be made a little more specific), so we just make these 4 files
a special case and negate the match with full filenames in src/.

Signed-off-by: Matt Sealey <matt@genesi-usa.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>

src/.gitignore

@@ -31,3 +31,7 @@ check-has-hidden-symbols.i
 check-link
 check-skiplist
 headers-standalone
+!cairo.pc.in
+!cairo-uninstalled.pc.in
+!cairo-features.pc.in
+!cairo-features-uninstalled.pc.in