Darwin: Actually stop the kernel build

Darwin: Actually stop the kernel build

At the moment, all of the kernel build lines end with "; true", which
means that the build will always continue, regardless of whether
creating an individual object file succeeds or not. The 'true' is there
to gobble up the name of the source file which the common build
infrastructure adds to the end of the command line.

Instead of using '; true', use '&& true', so that if one of the C
compiler commands, or the lipo, fails, we get told about it, before
we try to link the missing objects.

Change-Id: I11c14e6aa12188e3de044f900b3df8c8ffe5df13
Reviewed-on: http://gerrit.openafs.org/5391
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>