[RFA/commit/Win64] Remove new extra leading underscore in symbol name

[Joel Brobecker]

> Yes, by --enable-leading-mingw64-underscores just the default in bfd
> is changed. So it could be a work-a-round for supporting binaries
> having non-ABI name-decoration.

I'm afraid that this is what we're going to have to do.  One thing
we need to decide on, now, is whether 7.2 should build with the old
behavior by default or not.  If there hasn't been a GCC release
including the ABI change yet, then perhaps it's better for the users
if we tweak 7.2 to expect the non-ABI name-decorations.

-- 
Joel