Note that llvm::support::endianness has been renamed to
llvm::endianness while becoming an enum class as opposed to an
enum. This patch replaces support::{big,little,native} with
llvm::endianness::{big,little,native}.
Add branch/jump/call/l32r instructions and fixups support. Add R_XTENSA_32/R_XTENSA_SLOT0_OP
relocations in object files generation. Modify tests to support new instructions.
Add tests for relocations and fixups.
Differential Revision: https://reviews.llvm.org/D64836