I had a similar issue, the problem seems to occur here
nescc-mig java -java-classname=RssiMsg $< RssiMsg -o $@
.
The man page for nescc states that nescc is an extension for gcc. However, on OS X, clang runs instead of gcc. So instead of running gcc you are running clang.
If you have Mac ports you can install mp-gcc with $sudo port install mp-gcc46
and then run $sudo port select gcc mp-gcc46
. Trying running make <platform>
again and it should hopefully work.
Here's a guide on installing TinyOS on OS X just in case :) http://olafland.wordpress.com/2012/06/25/tinyos-on-mac-os-x-10-7-lion/