[X86,ARM] Retain split-stack prolog check for sibling calls

Summary:
If a routine with no stack frame makes a sibling call, we need to
preserve the stack space check even if the local stack frame is empty,
since the call target could be a "no-split" function (in which case
the linker needs to be able to fix up the prolog sequence in order to
switch to a larger stack).

This fixes PR37807.

Reviewers: cherry, javed.absar

Subscribers: srhines, llvm-commits

Differential Revision: https://reviews.llvm.org/D48444

llvm-svn: 335604