re PR middle-end/24295 (Xorg broken, #pragma weak foo = bar no longer causes bar to be referenced)

gcc/ChangeLog:
PR middle-end/24295
* cgraphunit.c (cgraph_varpool_remove_unreferenced_decls): Mark
alias targets.
* varasm.c (find_decl_and_mark_needed): After cgraph global info
is ready, stop marking functions, but still mark variables.
gcc/testsuite/ChangeLog:
PR middle-end/24295
* g++.old-deja/g++.abi/vtable2.C: Do not introduce external
declarations with the same names as thunks' alias targets, use
aliases instead.
* gcc.dg/attr-alias-3.c: New test.
* gcc.dg/weak/weak-14.c, gcc.dg/weak/weak-14a.c: New test.

From-SVN: r105688