[Bug modula2/117228] Move modula2 plugin into 'build-gcc/gcc/m2/'

[gaius at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117228

--- Comment #1 from Gaius Mulley <gaius at gcc dot gnu.org> ---
Created attachment 60358
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=60358&action=edit
Proposed patch containing documentation section and new example test code

This patch contains an additional section in gcc/doc/gm2.texi and
includes a new regression test gcc/testsuite/gm2/iso/run/lazyunique.mod.