Enable RV32 build of Linux/musl toolchain

[TommyMurphyTM1234]

With musl having been bumped to v1.2.5 recently:

• Bump musl from v1.2.2 to v1.2.5 #1568

it is now possible to enable the RV32 build of the Linux/musl toolchain.

• Bump musl from v1.2.2 to v1.2.5 #1568 (comment)

This PR effectively removes the restrictions imposed by this commit:

• 629c67e

I have checked that the "normal" (rv64gc/lp64d) and RV32 (rv32gc/ilp32d) configuration/builds of the Linux/musl toolchain complete successfully. At the moment there is no support for running the GCC test suite against the resulting toolchains so no further testing has been done.

Notes:

1. I'm not sure what was the rationale for/purpose of this PR a long time (6 years!) ago given that, at the time, musl did not have RV32 support.

• Allow building a 32bit musl toolchain #392

2. Even before this current PR --enable-multilib was being ignored due to this part of Makefile.in and this PR does not change this behaviour. Another PR can be done to deal with this if necessary.

• riscv-gnu-toolchain/Makefile.in

  Line 910 in 071f07c

  stamps/build-gcc-musl-stage2: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-musl-linux \

• riscv-gnu-toolchain/Makefile.in

  Line 934 in 071f07c

  --disable-multilib \

[cmuellner]

Thanks!

[TommyMurphyTM1234]

The change to this line in this PR seems to have got lost in the current master branch... :-(

• riscv-gnu-toolchain/configure.ac

  Line 144 in c4e32b3

  [build both RV32 and RV64 runtime libraries (only RV64 for musl libc) @<:@--disable-multilib@:>@])],

• 902bd3a