gnome-themes: enables the path to the icon-name-mapping to be specified

Ported a patch from sato-icon-theme which enables the path to the
icon-name-mapping tool to be specified to fix the build failure:
configure: error: icon-naming-utils >= 0.8.7 is required to build and install gnome-themes

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>