The generated code for a funclet can have an add to sp in the epilogue
for which there is no corresponding sub in the prologue.
This patch removes the early return from emitPrologue that was
preventing the sub to sp, and instead conditionalizes the appropriate
parts of the rest of the function.
Fixes https://bugs.llvm.org/show_bug.cgi?id=45345
Differential Revision: https://reviews.llvm.org/D77015
Daniel Frampton