libgnt/libgnt

Bump the minimum meson version to 0.56.0 and turn on additional warnings and fix them

2021-10-24, Gary Kramlich
86d548109b38
Bump the minimum meson version to 0.56.0 and turn on additional warnings and fix them

Testing Done:
Compiled

Reviewed at https://reviews.imfreedom.org/r/1095/
option('doc', type : 'boolean', value : true, yield : true,
description : 'build documentation with gtk-doc')
option('introspection', type : 'boolean', value : true, yield : true,
description : 'build introspection data')