DKMS failed to work after user defined/exported environmental variable 'ARCH'

It's accidentally found when doing a scripting installation.

To generate the issue:

1. export ARCH="amd64" or ARCH="x86_64"

2. apt-get install nvidia-current (or fglrx that uses DKMS)

This will cause the DKMS built failed. (for all module version with all kernels available in repo).

Error log in /var/lib/dkms/*/make.log

DKMS make.log for nvidia-current-304.88 for kernel 3.2.0-48-generic (x86_64)
Tue Jun 25 09:14:32 CEST 2013
make[1]: Makefile: No such file or directory
make[1]: *** No rule to make target `Makefile'. Stop.
make: *** [module] Error 2