Add dependence arc from running rustc to its libraries.

This commit fixes some oversights in the Makefile where rustc could be
invoked without some of its dependencies yet in place.  (I encountered
the problem in practice; its not just theoretical.)

As written in Makefile.in, $(STAGE$(1)_T_$(2)_H_$(3)) is the way one
writes an invocation of rustc where $(1) is the stage number $(2) is
the target triple $(3) is the host triple.  (Other uses of the macro
may plug in actual values or different parameters in for those three
formal parameters.)

When you have invocations of $(STAGE...), you need to make sure that
its dependences are satisfied; otherwise, if someone is using `make
-jN` for certain (large-ish) `N`, one can encounter situations where
GNU make attempts to invoke `rustc` before it has actually copied some
of its libraries into place, such as libmorestack.a, which causes a
link failure when the rustc invocation attempts to link in those
libraries.

In this case, the main prerequisite to add is TSREQ$(1)_T_$(2)_H_$(3),
which is described in Makefile.in as "Prerequisites for using the
stageN compiler to build target artifacts"

----

In addition to adding the extra dependences on TSREQ..., I also
replaced occurrences of the pattern:

    TSREQ$(1)_T_$(2)_H_$(3)
    $$(TLIB$(1)_T_$(2)_H_$(3))/$(CFG_STDLIB_$(2))
    $$(TLIB$(1)_T_$(2)_H_$(3))/$(CFG_EXTRALIB_$(2))

with:

    SREQ$(1)_T_$(2)_H_$(3)

which is equivalent to the above, as defined in Makefile.in

----

Finally, for the cases where TSREQ was missing in tests.mk, I went
ahead and put in a dependence on SREQ rather than just TSREQ, since it
was not clear to me how one could expect to compile those cases
without stdlib and extralib.

(It could well be that I should have gone ahead and done the same in
 other cases where I saw TSREQ was missing, and put SREQ in those
 cases as well.  But this seemed like a good measure for now, without
 needing to tax my understanding of the overall makefile
 infrastructure much further.)
Change libaux directory to fix aux crate tests on Windows
xfail tests that are currently failing on windows, reported in #7999
Generalize the `ty::substs` struct so that it can represent
multiple lifetime parameters, and not just one. Also add an option
for erasing lifetimes, which makes trans code somewhat simpler
and cleaner.
Check for comparisons to NaN in patterns

For every pattern that refers to a static value, evaluate it and emit a warning
if it is a NaN.

Fixes #6804
Generalize NaN pattern detection using walk_pat
rm unused upcall_exchange_free
rm default method lint

default methods are enabled by default, so there's not much point in
keeping around a lint to report them as being experimental
improve container/iterator tutorial
rewrite rust-mode to use font-lock-mode and emacs builtin syntax analysis
Convert uses of transmute which don't need it
syntax: Fix #6416 by aborting on errors after test parse.
Added some more atomic operations.
libstd: Implement {peer, socket}_name for new rt tcp & udp.
libstd: Fix errors when rtdebug! is not a noop.
libstd: Handle IPv4-Mapped/Compatible IPv6 addresses.
Add a function to check whether a ValueRef is a constant
Make omission of impossible if-else branches work with constants

Until now, we only optimized away impossible branches when there is a
literal true/false in the code. But since the LLVM IR builder already does
constant folding for us, we can trivially expand that to work with
constants as well.

Refs #7834
auto merge of #8027 : nikomatsakis/rust/issue-4846-multiple-lifetime-parameters-1, r=pcwalton

Small step towards #4846. r? @msullivan
NaN patterns: indicate that is_NaN is a method