Add OR operator for option '--with-extra-multilib-test'

This patch allows you provide the flags in build flags array acts on arch-abi
__respectively__, you can use ',' to separate them. For example:

`rv64gcv-lp64d:--param=riscv-autovec-lmul=dynamic,--param=riscv-autovec-preference=fixed-vlmax`

will be consider as two target boards same as below:

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

However, you can also leverage AND(`:`), OR(`,`) operator together but the
OR(`,`) will always have the higher priority. For example:

`rv64gcv-lp64d:--param=riscv-autovec-lmul=dynamic:--param=riscv-autovec-preference=fixed-vlmax,--param=riscv-autovec-lmul=m2`

will be consider as tow target boars same as below:

```
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=dynamic/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
```

Signed-off-by: Pan Li <pan2.li@intel.com>