Add pkg-config file for COGL

COGL should ship its own pkg-config file, obviously still pointing
to Clutter's compiler flags and linking options, for COGL-specific
variables that might be queried at configure time.

For instance, it's easier (and less verbose) to do:

  PKG_CHECK_EXISTS([cogl-gl-1.0],
                   [has_gl_backend=yes],
                   [has_gl_backend=no])

Than doing:

  AC_MSG_CHECKING([for GL support in COGL])
  cogl_backend=`$PKG_CONFIG --variable=cogl clutter-0.9`
  if test x$cogl_backend = xgl; then
    has_gl_backend=yes
    AC_MSG_RESULT([found])
  else
    has_gl_backend=no
    AC_MSG_RESULT([not found])
  fi

Makefile.am

@@ -2,6 +2,21 @@ SUBDIRS = common $(CLUTTER_COGL)
 
 BUILT_SOURCES = cogl.h
 
-EXTRA_DIST = cogl.h.in
+EXTRA_DIST = cogl.h.in cogl.pc.in
 
 DIST_SUBDIRS = common gl gles
+
+pc_files = \
+	cogl-$(CLUTTER_COGL)-$(CLUTTER_API_VERSION).pc \
+	cogl-$(CLUTTER_API_VERSION).pc
+
+cogl-$(CLUTTER_API_VERSION).pc: cogl.pc
+	$(QUIET_GEN)cp -f $< $(@F)
+
+cogl-$(CLUTTER_COGL)-$(CLUTTER_API_VERSION).pc: cogl.pc
+	$(QUIET_GEN)cp -f $< $(@F)
+
+pkgconfigdir = $(libdir)/pkgconfig
+pkgconfig_DATA = $(pc_files)
+
+CLEANFILES = $(pc_files)

cogl.pc.in

@@ -0,0 +1,15 @@
+prefix=@prefix@
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib
+includedir=${prefix}/include
+apiversion=@CLUTTER_API_VERSION@
+requires=@CLUTTER_REQUIRES@
+backend=@clutterbackend@
+cogl=@CLUTTER_COGL@
+
+Name: COGL
+Description: Clutter GL abstraction library (${cogl} backend)
+Version: @VERSION@
+Libs: -L${libdir} -lclutter-${backend}-${apiversion}
+Cflags: -I${includedir}/clutter-${apiversion}
+Requires: ${requires}