Modified libmng to depend on lcms and tell it where it can be found.

- Unfortunately libmng does not use pkg-config.

graphic/libmng/libmng.conf

@@ -12,6 +12,10 @@
 # GNU General Public License can be found in the file COPYING.
 # --- T2-COPYRIGHT-NOTE-END ---
 
+# Tell where to find lcms (pkg does not use pkg-config).
+pkgprefix -t lcms
+var_append GCC_WRAPPER_INSERT ' ' "-I$(pkgprefix includedir lcms) -L$(pkgprefix libdir lcms)"
+
 # for lib64 ...
 var_append makeinstopt ' ' "LIBPATH=$root/$libdir"