[PATCH 0/2] RISC-V: Support ELF attribute for GCC.

[Kito Cheng]

This patch series is implementation of RISC-V ELF attribute[1], it consists of
two part, first part is improve the -march string parser, in order to support
arch string with version and all kind of extension in the RISC-V ISA spec
v2.2[2], and second part is attribute directive generation, including configure
time and run time option to control that.

[1] https://github.com/riscv/riscv-elf-psabi-doc/pull/71
[2] https://github.com/riscv/riscv-isa-manual/blob/master/release/riscv-spec-v2.2.pdf