xcompile: Add core count to .xcompile

I think these four methods should cover most operating systems,
with many supporting several of the methods.

If we don't find anything, we're not any worse off than we were before.
The big issue would be if we get an incorrect value.

Change-Id: I4a612d39e93173e9d6e0de892f5bebf716912b1a
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12937
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
1 file changed