rework and optimize structure of Makefile.am

There were far too many intermediate libraries, references to obsolete
libtool bugs and whatnot.

We now have libcommon.la as a convenience archive that contains
spinlock, logging and misc stuff. A number of unit tests that need
those facilities are being linked to this.

Then we have libstacktrace.la convenience archive, since it is used by
libtcmalloc.la and libprofiler.la.

And after that we're simply directly creating our main library
products: libtcmalloc_minimal{,_debug}.la, libtcmalloc_{,debug}.la,
libprofiler.la etc.