[CIR] Fix emission of functions referenced by member-pointer (#181452)
While working on attributes for these, I discovered that when a function
was referenced only via a member function pointer (see no-odr-use.cpp
test for the example that failed!), that we were incorrectly generating
the type of the function to not include the 'this' pointer. This
restores that behavior by making sure we generate the type for the
member-pointer type correctly.