Windows: NSIS installer requires the architecture for CL=1400

Windows: NSIS installer requires the architecture for CL=1400

The NSIS installer at present is 32-bit only.  Production releases
of OpenAFS have always been performed using the CL=1310 compiler
so it wasn't noticed that src/WINNT/install/NSIS/NTMakefile did
not define the ARCH (architecture) for the purpose of identifying
which redistributable runtime library installer should be
integrated into the build.  For the CL=1310 compiler there are
not prebuilt installers for OpenAFS to integrate.

Change-Id: Ide80d5013f55dbcd97b7b099de7066c5afd0df14
Reviewed-on: http://gerrit.openafs.org/3388
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>