[RISCV] Missing cfi_def_cfa_offset?

For some stack adjustmnets, the RISC-V backend may emit a 2 adjustments of the stack pointer without a cfi_def_cfa_offset between them. This occurs when the stack adjust is roughly between +/-2048 and +/-4096. In that case we use 2 ADDIs instead of LUI+ADDI+ADD. gcc does something similar, but issues a cfi_def_cfa_offset between them. Should LLVM be emitting a cfi_def_cfa_offset

Example comparing llvm and gcc https://godbolt.org/z/eh63zn7b1

CC: @lenary @ilovepi @MaskRay @preames

Start with the RISC-V backend's stack-adjustment and CFI emission paths; the issue names no source file or test. Reproduce the Godbolt comparison, trace the two-ADDI case, and identify the relevant regression-test location. Done means the intended CFI behavior is established and covered for this adjustment range.

Written by the indexing model from the issue text.