avro

AVRO-894. C: cmake build now works on Mac OS X Lion

Before we were mistakenly setting CMAKE_OSX_ARCHITECTURES to our default
value, even if the user provided an override.  And our default included
"ppc", which borked on Lion since it doesn't include PowerPC compilers
in the Developer Tools.


git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1175560 13f79535-47bb-0310-9956-ffa450edef68