fix multilib support and rework --with-extra-multilib-test

[ewlu]

This pull request allows the following functionality:

1. Enable multilib support with generate_target_board.py and allow additional testing configurations without needing --with-extra-multilib-test flag
2. Enable linux multilib support using --with-multilib-generator

---

Currently --with-multilib-generator with more than one target is not supported with generate_target_board.py. For example,

  $ ../configure --prefix=/scratch/ewlu/ci/triage/other/build-newlib --with-multilib-generator="rv64gcv-lp64d--;rv32gcv-ilp32d--"

will have an error

usage: generate_target_board [-h] --sim-name SIM_NAME --build-arch-abi
                             BUILD_ARCH_ABI
                             [--extra-test-arch-abi-flags-list EXTRA_TEST_ARCH_ABI_FLAGS_LIST]
                             [--cmodel CMODEL]
generate_target_board: error: unrecognized arguments: rv32gcv-ilp32d

This is because generate_target_board expects rv32gcv-ilp32d to be passed in through --with-extra-multilib-test.

We fix generate_target_board.py's problem with multilib by changing the script arguments to accept a list of different configurations while maintaining the internal logic

For example, instead of running configure flags
--with-arch=rv64gc --with-abi=lp64d --with-extra-multilib-test="rv64gcv-lp64d:--param=riscv-autovec-lmul=dynamic:--param=riscv-autovec-preference=fixed-vlmax;rv64gcv_zba-lp64d"
to generate

riscv-sim/-march=rv64gc/-mabi=lp64d/-mcmodel=medlow
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=dynamic/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zba/-mabi=lp64d/-mcmodel=medlow

we can run
--with-multilib-generator="rv64gc-lp64d--;rv64gcv-lp64d--:--param=riscv-autovec-lmul=dynamic:--param=riscv-autovec-preference=fixed-vlmax;rv64gcv_zba-lp64d--
to generate the same boards
Alternatively, if we just want to run one target, the new flag --with-test-flags enables single target flexibility so
--with-arch=rv64gcv --with-abi=lp64d --with-test-flags="--param=riscv-autovec-lmul=dynamic:--param=riscv-autovec-preference=fixed-vlmax"
will generate target board

riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=dynamic/--param=riscv-autovec-preference=fixed-vlmax

---

--with-multilib-generator="<targets>" will fail with make report-linux because the desired targets will always be overwritten with the defaults (therefore testing incorrect targets). This supports the intended linux multilib builds and tests.

[patrick-rivos]

This is cool - I like the unified syntax for --with-multilib-generator and --with-extra-multilib-test. Specifying the flags lets us run multilibs where all the multilibs have options specified (we don't need to test a dummy config if we're only interested in --param=riscv-autovec-preference=fixed-vlmax). Adding --with-test-flags also makes sense to me.

For my own understanding @kito-cheng is the only difference between --with-multilib-generator and --with-extra-multilib-test that --with-extra-multilib-test doesn't build a new glibc for each mutilib?

[kito-cheng]

For my own understanding @kito-cheng is the only difference between --with-multilib-generator and --with-extra-multilib-test that --with-extra-multilib-test doesn't build a new glibc for each mutilib?

--with-multilib-generator will pass to GCC to configure the multilib, and it only support -mabi, -march and -mcmodel for the multilib selection.

For linux toolchain, we only use -mabi for the multilib selection, so it's not really make too much sense to configure linux toolchain with --with-multilib-generator="rv64gc-lp64d--;rv64gcv-lp64d--:--param=riscv-autovec-lmul=dynamic:--param=riscv-autovec-preference=fixed-vlmax;rv64gcv_zba-lp64d--, because rv64gc-lp64d--, rv64gcv-lp64d-- and rv64gcv_zba-lp64d-- are all mapping to /lib/lp64d.