Put tcmalloc first in Kernel linker list.

Ensures that the custom tcmalloc replacement takes over the work of malloc
everywhere on the system.

Other required changes:
 - Remove the unnecessary linking of all dependencies to every library. It
   is sufficient to link the 'global' dependencies to Kernel as this is linked
   to everything.
 - The Python libraries must also force loading tcmalloc first as they preload
   other libraries to avoid other bugs.

Refs #7748