libostree: Expose $OSTREE_FEATURES in the pkg-config file

This allows consumers of libostree to check at configure time whether it
supports the feature they want.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #832
Approved by: cgwalters

src/libostree/ostree-1.pc.in

@@ -2,6 +2,7 @@ prefix=@prefix@
 exec_prefix=@exec_prefix@
 libdir=@libdir@
 includedir=@includedir@
+features=@OSTREE_FEATURES@
 
 Name: OSTree
 Description: Git for operating system binaries