Add a pkgconfig file for uninstalled builds

This allows systems certain types of build setups to work. Specifically, this
will help when building on Android and using json-c as a dependency for another
package.

configure.in

@@ -35,6 +35,7 @@ AC_CONFIG_FILES([
 Makefile
 json.pc
 tests/Makefile
+json-uninstalled.pc
 ])
 
 AC_OUTPUT

json-uninstalled.pc.in

@@ -0,0 +1,11 @@
+prefix=
+exec_prefix=
+libdir=@abs_top_builddir@
+includedir=@abs_top_srcdir@
+
+Name: json
+Description: JSON implementation in C
+Version: @VERSION@
+Requires:
+Libs:  -L@abs_top_builddir@ -ljson
+Cflags: -I@abs_top_srcdir@