libgd: fix version in generated pkg-config .pc file

With the previous change to cmake, the generated pkg-config .pc
file does not contain the library version anymore. This breaks
programs which checks for a specific version, e.g. upcoming PHP 7.4.

The version is not filled because of a variable misnaming,
which was not covered by the imported upstream patch.

To not mangle the upstream patch, add an additional patch to
fix things up.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

libs/libgd/patches/300-gdlib.pc-cmake.patch

@@ -0,0 +1,11 @@
+--- a/config/gdlib.pc.cmake
++++ b/config/gdlib.pc.cmake
+@@ -5,7 +5,7 @@ includedir=${prefix}/@CMAKE_INSTALL_INCL
+ 
+ Name: gd
+ Description: GD graphics library
+-Version: @GDLIB_VERSION@
++Version: @GD_VERSION@
+ Cflags: -I${includedir}
+ Libs.private: @LIBGD_DEP_LIBS@
+ Libs: -L${libdir} -lgd