Support: Document Endian.h functions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204671 91177308-0d34-0410-b5e6-96231b3b80d8
DebugInfo: Add DW_AT_GNU_ranges_base to skeleton CUs

This is used to avoid relocations in the dwo file by allowing
DW_AT_ranges specified in debug_info.dwo to be relative to this base
address. (r204667 implements the base-relative DW_AT_ranges side of
this)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204672 91177308-0d34-0410-b5e6-96231b3b80d8