Excludes ppc64 from kext support tools build.

Due to some as yet not understood bug, recent builds (>=V2.6.2)
of these tools have contained broken ppc64 content, resulting
in unusability on G5s.  This change excludes the broken content,
and has no effect on builds for >=10.6, where PPC is unsupported.

Although the bad builds (presumably under Xcode 3.2) are not
reproducible here, the effect of omitting the ppc64 "forks"
has been tested with Xcode 3.1.