Add documentation for Multilib custom flags (#114998)

This patch is the fourth step to extend the current multilib system to
support the selection of library variants which do not correspond to
existing command-line options.

Proposal can be found in
https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

The multilib mechanism supports libraries that target code generation or
language options such as --target, -mcpu, -mfpu, -mbranch-protection.
However, some library variants are particular to features that do not
correspond to any command-line options. Examples include variants for
multithreading and semihosting.

This work introduces a way to instruct the multilib system to consider
these features in library selection. This particular patch updates the
documentation.

0 files changed, 0 insertions, 0 deletions