src: make sort order deterministic, next try

We cannot compare pointers as they may point to qsort-local objects.
And we must make sure that cmp(a,b) always agrees with cmp(b,a).

src/linker.cpp

@@ -329,6 +329,7 @@ ElfLinker::Section *ElfLinker::addSection(const char *sname, const void *sdata,
     assert(sname[strlen(sname) - 1] != ':');
     assert(findSection(sname, false) == nullptr);
     Section *sec = new Section(sname, sdata, slen, p2align);
+    sec->sort_id = nsections;
     sections[nsections++] = sec;
     return sec;
 }