Before the last patch, we had an efficient loop that disabled
local breakpoints on task switch. Re-add that, but in a more
general way that handles changes to the global enable bits too.
Backports commit 36eb6e096729f9aade3a6af7dbe4d0a990335d7e from qemu
This moves the last of the iteration over breakpoints into
the bpt_helper.c file. This also allows us to make several
breakpoint functions static.
Backports commit 93d00d0fbe4711061834730fb70525d167b6f908 from qemu
