change ABI_VERSION back to just include the major number

change ABI_VERSION back to just include the major number

By default, GCC hard codes the name for ld.so to /lib/ld-uClibc.so.0
so our default should match that. If distribution makers want to change
it, they need to change the default gcc configuration as well.

Signed-off-by: Austin Foxley <austinf@cetoncorp.com>