[Bug modula2/107612] plugin/m2rte doesn't build on Mac OS X 10.7

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107612

--- Comment #4 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Rainer Orth from comment #1)
> Besides, the m2rte plugin is incorrectly named on Darwin, thus unusable:
> 
> cc1gm2: fatal error: inaccessible plugin file
> /var/gcc/modula-2/10.7-gcc/./gcc/plugin/m2rte.dylib expanded from short
> plugin name m2rte: No such file or directory
> compilation terminated.
> 
> There's code in gcc/jit/Make-lang.in handling the same situation.
> 
> To get further along, I've just manually added a symlink for now.


Hi Rainer, you are ahead of me in testing this (I got bogged down in fixing
libffi for i686 rust use)

Just to note that the values used in gcc/jit/Make-lang.in are still not
completely correct (and that causes problems with cross-compilers where the
target and host linkers are different)

 * because LD_VERSION_SCRIPT_OPTION and LD_SONAME_OPTION are for $target, not
$host.
 * (maybe not relevant to gm2) the .map file is not in a format usable by
Darwin's linker and unfortunately the existing conversion scripts in the tree
do not handle that specific map.

So much of the content is useful for Darwin and mingw but those points need to
be taken into account (rather than copying verbatim).