Since Apple LLVM no longer reports which version of LLVM it's based off (starting with 7.0.0), I believe it's time to start checking Apple LLVM versions directly.
The changes in this pull request update the `configure` script to check "Apple LLVM" versions independently if no "based off" version can be found. If a "based off" version is included, however, it will be preferred.
(This is a less hacky version of #26653)
This PR will enable RUSTC to generate PDB debuginfo files when targeting the MSVC toolchain. Mind that these are not full featured PDB files -- they just contain line tables, so you can get proper backtraces and step through your code, but variable values can't be inspected. We are just levering (LLVM's current support)[http://clang.llvm.org/docs/MSVCCompatibility.html] for creating Windows debuginfo. When LLVM's support gets better, we should benefit from that too without much effort.
I also wanted to include some kind of auto test with this PR but I could not get the `rmake` tests to work properly when targeting MSVC.
EDIT:
Closes#19533
Currently errorck yields bogus `duplicate error code` messages when an error code occurs inside of a long diagnostic message (see https://github.com/rust-lang/rust/pull/26982), because errorck just goes line by line checking for error codes and recording them all.
A simplistic approach to fixing this is just to detect the beginning of a long diagnostic raw string literal (`r##"`) and skip lines until the end of the raw string literal is encountered. I'm not completely confident in this approach, but I think a more robust approach would be more complicated and I wanted to get feedback before pursuing that.
... matching the existing Index impls.
There is no reason not to if String implement DerefMut.
The code removed in `src/librustc/middle/effect.rs` was added in #9750
to prevent things like `s[0] = 0x80` where `s: String`,
but I belive became unnecessary when the Index(Mut) traits were introduced.
