Fix bad architecture detection on Raspbian Wheezy

Ref: Issue #652 (but not sure how to re-open the issue).

On Raspbian Wheezy (on my system), there is no "vendor_id" in the /proc/cpuinfo
so the regex on line 94:

    regexp = re.compile(r"^vendor_id\s+:\s*(?P<vendorid>\S+)\s*$", re.M)

will fail, and there will be no groupdict() returned from the immediately
following line:

    result = regexp.search(txt).groupdict()

So I wrapped this in a "try/except AttributeError" and so that this could proceed to the ARM detection.

With these edits, EasyBuild proceeds smoothly to compile GCC on my Raspberry Pi.