build numpy from source results in wrong architecture

Question

I build numpy from source on my mac to link it to my ATLAS library. Thus, I wanted to run it as described here with these options:

export MACOSX_DEPLOYMENT_TARGET=10.10
export CFLAGS="-arch i386 -arch x86_64"
export FFLAGS="-m32 -m64"
export LDFLAGS="-Wall -undefined dynamic_lookup -bundle -arch i386 -arch x86_64"
export PYTHONPATH="/Library/Python/2.6/site-packages/"

But the compiler didn't like all of these arch flags and exited with:

C compiler: cc -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -arch x86_64 -arch i386 -pipe

compile options: '-c'
cc: _configtest.c
cc _configtest.o -L/usr/local/atlas/lib -llapack -lf77blas -lcblas -latlas -o _configtest
ld: warning: ignoring file _configtest.o, file was built for i386 which is not the architecture being linked (x86_64): _configtest.o
Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

I could make the installation work when removing the -arch i386 flag:

cc -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -arch x86_64 -pipe

But this results in an error, when importing numpy:

>>> import numpy
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Python/2.7/site-packages/numpy/__init__.py", line 170, in <module>
    from . import add_newdocs
  File "/Library/Python/2.7/site-packages/numpy/add_newdocs.py", line 13, in <module>
    from numpy.lib import add_newdoc
  File "/Library/Python/2.7/site-packages/numpy/lib/__init__.py", line 8, in <module>
    from .type_check import *
  File "/Library/Python/2.7/site-packages/numpy/lib/type_check.py", line 11, in <module>
    import numpy.core.numeric as _nx
  File "/Library/Python/2.7/site-packages/numpy/core/__init__.py", line 6, in <module>
    from . import multiarray
ImportError: dlopen(/Library/Python/2.7/site-packages/numpy/core/multiarray.so, 2): no suitable image found.  Did find:
    /Library/Python/2.7/site-packages/numpy/core/multiarray.so: mach-o, but wrong architecture

My arch is in fact i386 and my machine a x86_64h.

Does this mean, that I installed a wrong ATLAS or am I missing something in the numpy build? Why do I have to pass multiple -arch flags?