[BUG] Failing to compile: program does not contain a static `main' method

[AstralShadow]

Describe the bug
I'm getting 'error: program does not contain a static `main' method' when compiling with:

• valac 0.56.4
• cmake 3.25.3
• gettext 0.21.1
• gtk+ 3.24.37
• glib 2.74.6
• libcanberra 0.30-r7
• libpeas 1.34.0
• libayatana-appindicator 0.5.92

To Reproduce
Steps to reproduce the behavior:

1. git clone https://github.com/JMoerman/Go-For-It.git
2. cd Go-For-It/
3. mkdir build
4. cd build
5. cmake -D VALA_EXECUTABLE='/usr/bin/vala-0.56' ..
6. make

Expected behavior
Successful compilation.

Screenshots

The upper half is the console output i get when trying to compile.
The lower half contains the line that throws the error.

Command line output

error: program does not contain a static `main' method
make[2]: *** [src/CMakeFiles/com.github.jmoerman.go-for-it-0.dir/build.make:312: src/com.github.jmoerman.go-for-it-0_valac.stamp] Error 1
make[1]: *** [CMakeFiles/Makefile2:204: src/CMakeFiles/com.github.jmoerman.go-for-it-0.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

OS and application version:
OS: Gentoo
Application version: latest upstream / git: 0edb744

Additional context

Gentoo provides USE-flags which allows personalizing some compile-time flags for some applications.
That means it's possible that some of the dependencies i have installed may not contain everything you'd expect from a general build, but i don't think i'm disabling anything that might be necessary. (I believe the static main method that the error mentions should be withing Go-For-It's code, but i got no experience working with vala or GTK/GTK+, so correct me if i'm wrong)
I double checked my USE flags and i'm sure i set decent configuration there.

[AstralShadow]

How should i approach debugging my issue?