[PATCH 1/3] RISC-V: Handle implied extension in canonical ordering.

- ISA spec has specify the order between multi-letter extensions, implied extension also need to follow store in canonical ordering, so most easy way is we keep that in-order during insertion. gcc/ChangeLog: * common/config/riscv/riscv-common.c (single_letter_subset_rank): New.

[PATCH 1/3] RISC-V: Handle implied extension in canonical ordering.

- ISA spec has specify the order between multi-letter extensions, implied extension also need to follow store in canonical ordering, so most easy way is we keep that in-order during insertion. gcc/ChangeLog: * common/config/riscv/riscv-common.c (single_letter_subset_rank): New.