[Coverage] Fix the start/end locations of switch statements

While pushing switch statements onto the region stack we neglected to
specify their start/end locations. This results in a crash (PR26825) if
we end up in nested macro expansions without enough information to
handle the relevant file exits.

I added a test in switchmacro.c and fixed up a bunch of incorrect CHECK
lines that specify strange end locations for switches.

llvm-svn: 262697