I found a line like this in the file:

numpy/distutils/fcompiler/__init__.py

I changed the -2 to 2, but it didn't change anything. In fact, this
line wasn't called.

The fct set_verbosity() is called only once, with the value of 0. The
default value set at import. If I change that to 2 or -2, it do not
change anything.

I think that the problem is related to the exec_command as you told.
It seam it call it in a way that don't take the stdout/stderr set in
Python. So I can't redirect it. The problem is that is use os.system()
and we can't redirect its stdout/stderr.

What about replacing the os.system call to  subprocess.Popen? This
would allow us to catch the stdout/stderr. We use this call in Theano
and it is compatible with python 2.4.