rustc: Deterministically link upstream C libraries

Previously, upstream C libraries were linked in a nondeterministic fashion
because they were collected through iter_crate_data() which is a nodeterministic
traversal of a hash map. When upstream rlibs had interdependencies among their
native libraries (such as libfoo depending on libc), then the ordering would
occasionally be wrong, causing linkage to fail.

This uses the topologically sorted list of libraries to collect native
libraries, so if a native library depends on libc it just needs to make sure
that the rust crate depends on liblibc.
auto merge of #13463 : alexcrichton/rust/c-linkage-oh-my, r=brson

Previously, upstream C libraries were linked in a nondeterministic fashion
because they were collected through iter_crate_data() which is a nodeterministic
traversal of a hash map. When upstream rlibs had interdependencies among their
native libraries (such as libfoo depending on libc), then the ordering would
occasionally be wrong, causing linkage to fail.

This uses the topologically sorted list of libraries to collect native
libraries, so if a native library depends on libc it just needs to make sure
that the rust crate depends on liblibc.