custom_target ignores deps with ninja backend

[phako]

Try running test cases/vala/9 gir the following way:

cd test cases/vala/9 gir
mkdir _build
cd _build
meson ..
ninja Foo-1.0.typelib
ninja: error: '/home/jens/Source/meson/test cases/vala/9 gir/_build/Foo-1.0.gir', needed by 'Foo-1.0.typelib', missing and no known rule to make it

Ninja does not seem to know that it has to build the dependency declared in deps

[phako]

Btw, I'm not sure it is specifc to vala or gnome, I think custom_target has an issue with interpreting deps properly

[phako]

I looked a bit deeper. The gir target will declare an output artifact Foo-1.0.gir in its ninja rule, but then the rule for generating the typelib will be written with "/full/path/to/gir/in/build/Foo-1.0.gir" due to meson.current_build_dir() being returning the full path - that doesn't match up. If I manually remove the full path from the build file, ninja is happy.