do not determine number of iterations in easyblock constructor (which is too early), but in run_all_steps

[branfosj]

#4919 calls det_iter_cnt() too early.

If we call det_iter_cnt() in the __init__ then we do this before we initialise the easyblock for the specific bit of software, so we do not know how many iterations there are. This means we fix on one iteration.

[boegel]

Without this fix, the installation of GCCcore is broken, because not enough iterations are being done in the build.

More specifically, the additional build stages that the easyblock should do for the nvptx and amdgcn OpenMP offload targets were no longer being done, because the changes to configopts and buildopts that are done in run_all_steps in the custom easyblock for GCC were being done after det_iter_cnt was called.
That lead to some part of the GCC installation being missing, which was caught by the sanity check:

== FAILED: Installation ended unsuccessfully: Sanity check failed: no file found at 'bin/nvptx-none-as' in /tmp/software/GCCcore/13.3.0

@branfosj Thanks a lot for figuring this out!

[boegel]

This bug also affects other software-specific easyblocks where we get creative with iterations, like FFTW, GROMACS, ELPA

[boegel]

lgtm