Set rv64gc the default for --with-arch option.

[pz9115]

This PR updates the default option of --with-arch from rv64imafdc to rv64gc. In newer gcc versions, gc is equivalent to imafdc_zicsr_zifencei, which provides CSR instructions reading from and writing to CSRs(Zicsr) and fence instruction ensuring memory consistency between code and data(Zifencei).

Most Linux distributions (such as Debian Arch, Gentoo for RISC-V) use the rv64gc architecture when building RISC-V user space and kernel to ensure that system-level applications have the necessary instruction support now.

And most RISC-V development boards now also set gc as their default supported arch.

[TommyMurphyTM1234]

Should it also be changed here, perhaps?

• riscv-gnu-toolchain/configure.ac

  Line 176 in c4e32b3

  [AC_SUBST(glibc_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 180 in c4e32b3

  [AC_SUBST(newlib_multilib_names,"rv32i-ilp32 rv32iac-ilp32 rv32im-ilp32 rv32imac-ilp32 rv32imafc-ilp32f rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 184 in c4e32b3

  [AC_SUBST(musl_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 184 in c4e32b3

  [AC_SUBST(musl_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

[pz9115]

Should it also be changed here, perhaps?

• riscv-gnu-toolchain/configure.ac

  Line 176 in c4e32b3

  [AC_SUBST(glibc_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 180 in c4e32b3

  [AC_SUBST(newlib_multilib_names,"rv32i-ilp32 rv32iac-ilp32 rv32im-ilp32 rv32imac-ilp32 rv32imafc-ilp32f rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 184 in c4e32b3

  [AC_SUBST(musl_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

• riscv-gnu-toolchain/configure.ac

  Line 184 in c4e32b3

  [AC_SUBST(musl_multilib_names,"rv32imac-ilp32 rv32imafdc-ilp32d rv64imac-lp64 rv64imafdc-lp64d")],

Thanks for the reminder, I think it needs a new PR, since the current one may not be accepted XD

[TommyMurphyTM1234]

Thanks for the reminder, I think it needs a new PR, since the current one may not be accepted XD

Why not?

[kito-cheng]

LGTM, and I am OK with the separate PR for the multilib stuff updating, thanks Jiawei :)