This patch adds tail call support to the LoongArch backend. When
appropriate, use the `b` or `jr` instruction for tail calls (the
`pcalau12i+jirl` instruction pair when use medium codemodel).
This patch also modifies the inappropriate operand name:
simm26_bl -> simm26_symbol
This has been modeled after RISCV's tail call opt.
Reviewed By: SixWeining
Differential Revision: https://reviews.llvm.org/D137889
In LoongArch, when `CodeModel=Medium`, it just increases the jumping
ability of function calls relative to PC, from 2^28 to 2^32.
Depends on D137393
Reviewed By: SixWeining
Differential Revision: https://reviews.llvm.org/D137394