[ARM] GlobalISel: Add support for i32 modulo

Add support for modulo for targets that have hardware division and for
those that don't. When hardware division is not available, we have to
choose the correct libcall to use. This is generally straightforward,
except for AEABI.

The AEABI variant is trickier than the other libcalls because it
returns { quotient, remainder }, instead of just one value like the
other libcalls that we've seen so far. Therefore, we need to use custom
lowering for it. However, we don't want to have too much special code,
so we refactor the target-independent code in the legalizer by adding a
helper for replacing an instruction with a libcall. This helper is used
by the legalizer itself when dealing with simple calls, and also by the
custom ARM legalization for the more complicated AEABI divmod calls.

llvm-svn: 305459