the 'n' in armv7hnl is for NEON optimisation. This is how you're setting up you're CFLAGS and nothing to do with IoT (or likely even Fedora arm)

Shouldn't just calling pkg-config somepackage from the command line work?

Originally, I wanted to compile something in Rust with Cargo which needs C flags and calls:

  --- stderr
  thread 'main' panicked at 'Pkg-config failed - usually this is because alsa development headers are not installed.
  For Fedora users:
  # dnf install alsa-lib-devel
  For Debian/Ubuntu users:
  # apt-get install libasound2-dev
  pkg_config details:
  `"pkg-config" "--libs" "--cflags" "alsa"` did not exit successfully: exit code: 127
  --- stderr
  /usr/bin/pkg-config: line 8: /usr/bin/armv7hnl-redhat-linux-gnueabi-pkg-config: No such file or directory
  ', /var/home/user/.cargo/registry/src/github.com-1285ae84e5963aae/alsa-sys-0.3.1/build.rs:6:50

Just to be clear: This is NOT cross-compiling.

I am no expert in compiling and don't know what to do, i would just expect it to work.

Well arm builds work for me, I don't do them on IoT edition, but i do them basically daily on Fedora arm, and we do 100s a day on the build infrastructure.

Doing builds on a ostree platform is likely not the best way, you should likely use a container on top or something.

The compilers work just fine, but you've not outlined what you've installed, how you're trying to do it or or basically anything, and this isn't really the place to file build issues.