README.md prerequisites section is incomplete

[TommyMurphyTM1234]

The list of prerequisite packages required to build the toolchain (and run the test suite etc.) here seems incomplete:

• https://github.com/riscv-collab/riscv-gnu-toolchain#prerequisites

The following is a list of additional prerequisites that are needed in certain circumstances - initially for Ubuntu (I'm using Zorin OS Lite 16.3 - a Ubuntu 20.04.1 LTS derivative) but I will try to identify the equivalent packages for other distros/platforms once I have identified all omissions first.

• git - now listed in the prerequisites section of README.md
• If using multilibs (configure --with-multilib-generator or configure --enable-multilib) (?):
  • python-is-python3 - needed in addition to python3 which is already in the prerequisites list
    • see here: execvp: /bin/sh: Argument list too long error when using with --with-multilib-generator #1226 (comment)
• If running the test suite
  • expect
  • Python pyelftools
  • Spike only?
    • device-tree-compiler
  • QEMU only?
    • libglib2.0-dev
    • pip
• More to come if necessary...

[TommyMurphyTM1234]

Not sure about this but another potential dependency?
If GDB Python support is needed then one of the following pairs?
(Not sure how this aligns with pther Python dependencies specified previously?)

• python and python-dev
• python2 and python2-dev
• python3 and python3-dev

See here:

• how to enable python for gdb #925
• GDB built on Ubuntu 20.04 is missing Python support #722

[cmuellner]

I'm fine with adding additional dependencies as long as we also list them in the CI/CD script.

But I don't think we should install a Python 2 package. It would be a waste of time to support it.