[COFF, ARM64] Remove definitions for _byteswap library functions

_byteswap_* functions are are implemented in below file as normal function
from libucrt.lib and declared in stdlib.h. Define them in intrin.h triggers
lld error "conflicting comdat type" and "duplicate symbols" which was just
added to LLD (https://reviews.llvm.org/D57324).

C:\Program Files (x86)\Windows Kits\10\Source\10.0.17763.0\ucrt\stdlib\byteswap.cpp

Differential Revision: https://reviews.llvm.org/D57915

llvm-svn: 353740