UGP contains the pointer for thread data:
> The TLS area is accessed at the processor level through the special
register UGP This register is set to the address one location above the
TLS area, which grows downwards from UGP.
From the Hexagon ABI spec -
https://docs.qualcomm.com/bundle/publicresource/80-N2040-23_REV_K_Qualcomm_Hexagon_Application_Binary_Interface_User_Guide.pdf
Also: disable clang-format for `NodeType` enum in
`llvm/lib/Target/Hexagon/HexagonISelLowering.h` to avoid disruptive
formatting.
