Add separate build_id.cc.in for client library.  This will silence SCons
warning.

	modified:   SConstruct
	modified:   src/SConscript
	modified:   src/bruce/client/bruce_client.h
	new file:   src/bruce/client/build_id.c.in
	new file:   src/bruce/client/build_id.h
	modified:   src/bruce/client/libbruce_client.c