[GlobalISel][CallLowering] Don't tail call with non-forwarded explicit sret

Similar to this commit:

faf8065a

Testcase is pretty much the same as

test/CodeGen/AArch64/tailcall-explicit-sret.ll

Except it uses i64 (since we don't handle the i1024 return values yet), and
doesn't have indirect tail call testcases (because we can't translate those
yet).

Differential Revision: https://reviews.llvm.org/D86148