[EH] Rename llvm.x86.seh.recoverfp intrinsic to llvm.eh.recoverfp

Summary:
Make recoverfp intrinsic target-independent so that it can be implemented for AArch64, etc.
Refer D53541 for the context. Clang counterpart D56748.

Reviewers: rnk, efriedma

Reviewed By: rnk, efriedma

Subscribers: javed.absar, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D56747

llvm-svn: 351281