[Bug lto/48447] LTO link fails to link libgcc correctly when -nostdlib option is specified

["davek at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48447

--- Comment #5 from Dave Korn <davek at gcc dot gnu.org> 2011-04-07 15:49:29 UTC ---
Well, this is basically a weakness in the pass-through solution implemented for
PR 42690; it only knows about the compilers stdlibs, and doesn't process any
user-specified libs on the command line.  In the general case that's how things
ought to be: LTRANS only generates new references to builtins/libcalls, not any
of the user's code.  However when you use -nostdlib and pass libgcc as if it
were a user library, as in case 3, the pass-through mechanism doesn't know that
it's actually a compiler runtime rather than user library and doesn't pass it
through.

The correct fix is going to be in the linker, not the compiler, by implementing
a second library scan pass and obsoleting the pass-through mechanism.  I've got
a revised version of that experimental patch that I'll attach to this PR for
reference.