fix compilation errors of mips target
auto merge of #9277 : crabtw/rust/mips, r=brson

This patch fixes some errors of MIPS target, however, MIPS C ABI is still broken. I will send another PR to fix the problem.

Because MIPS target has no "generic" CPU name, I add --target-cpu and --target-feature to RUST_FLAGS. In order to workaround the "compact frame descriptions incompatible with DWARF2 .eh_frame" problem, the linker I used is CXX but not CC.
Register new snapshots
auto merge of #9296 : alexcrichton/rust/snapshots, r=cmr

huzzah!
lexer: show correct span on lexical errors

Previously, the lexer calling `rdr.fatal(...)` would report the span of
the last complete token, instead of a span within the erroneous token
(besides one span fixed in 1ac90bb).

This commit adds a wrapper around `rdr.fatal(...)` that sets the span
explicilty, so that all fatal errors in `libsyntax/parse/lexer.rs` now
report the offending code more precisely. A number of tests try to
verify that, though the `compile-fail` testing setup can only check that
the spans are on the right lines, and the "unterminated string/block
comment" errors can't have the line marked at all, so that's incomplete.

Closes #9149.
lexer: report problematic chars verbatim or as escape sequence

... instead of giving their numeric codepoint, following the lead of
fdaae34. So the error message for, say, '\_' mentions _ instead of 95,
and '\●' now mentions \u25cf.
lexer: have all lexer errors report the offending code directly