gn: Add recipe

gn: Add recipe

gn is a commonly used build tool to generate ninja files, used
in a lot of recipes e.g. chromium, qtwebengine, perfetto, hafnium etc.
these recipes come from different layers e.g. meta-qt6/meta-arm/meta-oe

since not all layers depend on meta-oe ( meta-arm does not ), its not
a possible option.

Given the usecases, putting it in core will benefit the ecosystem
and reduce some duplication. This recipe is taken from meta-arm

Disable maybe-initialized is a gcc specific option as error

Disable format warnings as errors, it adds -Wno-format explictly in
its build system

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>