mention that 'extern crate compiler_builtins' must be used
in some crate that's part of the dependency graph of the crate one's
building.
r? @alexcrichton
test the mips64 targets
These should be all the required changes I think but libloading can't be cross compiled for these new targets:
```
error: failed to run custom build command for `libloading v0.3.1`
process didn't exit successfully: `/target/debug/build/libloading-07147fe7fffab0b2/build-script-build`(exit code: 101)
--- stderr
thread 'main' panicked at 'could not get target info: TargetNotFound', ../src/libcore/result.rs:799
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```
I've openend nagisa/rust_libloading#19 to track that. Wel'll have to wait until that's fixed.
cc @alexcrichton
Update CI configs
* Run on the master branch (to get previews)
* Pass --target on AppVeyor (oops)
* Use the current nightly for arm (I think that bug is fixed)
Initial implementation of multitester
Implements part of #72.
I wanted to work on this first because it should help me find the problem in the add implementation.
Test failures now look like this:
```
__addsf3 - Args: 1 1264853201
rustc-builtins: Some(0)
compiler_rt: Some(14950609)
gcc_s: None
__addsf3 - Args: 1 632426600
rustc-builtins: Some(0)
compiler_rt: Some(0.00000000000000030889195)
gcc_s: None
__addsf3 - Args: 1 316213300
rustc-builtins: Some(0)
compiler_rt: Some(0.0000000000000000000000000013696648)
gcc_s: None
[snip]
thread 'float::add::tests::_test::__addsf3' panicked at '[quickcheck] TEST FAILED. Arguments: (1, 1)', /home/matt/.cargo/registry/src/github.com-1ecc6299db9ec823/quickcheck-0.3.1/src/tester.rs:118
```
It currently prints all of the errors, if that's undesirable we'd need to remove the shrinkers or modify quickcheck.
due to how Cargo works, the rustc-cfg in build.rs was picking our target
specifications rather than the one the user meant to use. Placing our
target files in any place other than the root of the Cargo project
avoids the issue.
