This also removes existing patches that were trying to fix warnings
one-by-one.
Note that the patch making `CurrentSp` static was incorrect, the
variable needs to be on the stack for us to retrieve the current stack
address.
Also, update it to the latest revision, which makes it possible to build
without most of the patches we needed before, but now we need our own
definitions for LibC includes and to disable errors for the warning
bad-function-cast.
