MSYS2. rustc cannot link binaries. -- could not exec the linker `gcc`: Access is denied. (os error 5)

A binary linking to SDL2 fails

```
$ multirust run stable cargo run -j1 --verbose
multirust: checking metadata version
multirust: got metadata version 2
Compiling libc v0.2.10
Running `rustc E:/home/.multirust/toolchains/stable/cargo\\registry\\src\\github.com-88ac128001ac3a9a\\libc-0.2.10\\src\\lib.rs --crate-name libc --crate-type lib -g --cfg feature=\"use_std\" --cfg feature=\"default\" -C metadata=12d5d911cf5411c3 -C extra-filename=-12d5d911cf5411c3 --out-dir E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --cap-lints allow`
Compiling rustc-serialize v0.3.19
Running `rustc E:/home/.multirust/toolchains/stable/cargo\\registry\\src\\github.com-88ac128001ac3a9a\\rustc-serialize-0.3.19\\src\\lib.rs --crate-name rustc_serialize --crate-type lib -g -C metadata=d9e72695d437325f -C extra-filename=-d9e72695d437325f --out-dir E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --cap-lints allow`
Compiling rand v0.3.14
Running `rustc E:/home/.multirust/toolchains/stable/cargo\\registry\\src\\github.com-88ac128001ac3a9a\\rand-0.3.14\\src\\lib.rs --crate-name rand --crate-type lib -g -C metadata=6fab17fc670a2bc8 -C extra-filename=-6fab17fc670a2bc8 --out-dir E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --extern libc=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps\\liblibc-12d5d911cf5411c3.rlib --cap-lints allow`
Compiling lazy_static v0.1.16
Running `rustc E:/home/.multirust/toolchains/stable/cargo\\registry\\src\\github.com-88ac128001ac3a9a\\lazy_static-0.1.16\\src\\lib.rs --crate-name lazy_static --crate-type lib -g -C metadata=e69e55dcc7527931 -C extra-filename=-e69e55dcc7527931 --out-dir E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --cap-lints allow`
Compiling sdl2-sys v0.8.1
Running `rustc E:/home/.multirust/toolchains/stable/cargo\\registry\\src\\github.com-88ac128001ac3a9a\\sdl2-sys-0.8.1\\build.rs --crate-name build_script_build --crate-type bin -g --cfg feature=\"default\" --out-dir E:\\home\\rst_prj\\bnoise\\target\\debug\\build\\sdl2-sys-7d2af11caee603cd --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps -L dependency=E:\\home\\rst_prj\\bnoise\\target\\debug\\deps --cap-lints allow`
error: could not exec the linker `gcc`: Access is denied. (os error 5)
Could not compile `sdl2-sys`.

Caused by:
Process didn't exit successfully: `rustc E:/home/.multirust/toolchains/stable/cargo\registry\src\github.com-88ac128001ac3a9a\sdl2-sys-0.8.1\build.rs --crate-name build_script_build --crate-type bin -g --cfg feature="default" --out-dir E:\home\rst_prj\bnoise\target\debug\build\sdl2-sys-7d2af11caee603cd --emit=dep-info,link -L dependency=E:\home\rst_prj\bnoise\target\debug\deps -L dependency=E:\home\rst_prj\bnoise\target\debug\deps --cap-lints allow` (exit code: 101)
```

`build`ing a pure Rust library succeeds:

```
$ multirust run nightly cargo build -j1 --verbose
multirust: checking metadata version
multirust: got metadata version 2
Compiling scratchpad v0.1.0 (file:///E:/home/rst_prj/scratchpad)
Running `rustc src\\lib.rs --crate-name scratchpad --crate-type lib -g --out-dir E:\\home\\rst_prj\\scratchpad\\target\\debug --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\scratchpad\\target\\debug -L dependency=E:\\home\\rst_prj\\scratchpad\\target\\debug\\deps`
src\lib.rs:1:12: 1:16 warning: unused or unknown feature, #[warn(unused_features)] on by default
src\lib.rs:1 #![feature(test)]
```

But running its tests does not.

```
$ multirust run nightly cargo test -j1 --verbose
multirust: checking metadata version
multirust: got metadata version 2
Compiling scratchpad v0.1.0 (file:///E:/home/rst_prj/scratchpad)
Running `rustc src\\lib.rs --crate-name scratchpad --crate-type lib -g --test -C metadata=7603f6f9c621acdf -C extra-filename=-7603f6f9c621acdf --out-dir E:\\home\\rst_prj\\scratchpad\\target\\debug --emit=dep-info,link -L dependency=E:\\home\\rst_prj\\scratchpad\\target\\debug -L dependency=E:\\home\\rst_prj\\scratchpad\\target\\debug\\deps`
error: could not exec the linker `gcc`: Access is denied. (os error 5)
error: Could not compile `scratchpad`.

Caused by:
Process didn't exit successfully: `rustc src\lib.rs --crate-name scratchpad --crate-type lib -g --test -C metadata=7603f6f9c621acdf -C extra-filename=-7603f6f9c621acdf --out-dir E:\home\rst_prj\scratchpad\target\debug --emit=dep-info,link -L dependency=E:\home\rst_prj\scratchpad\target\debug -L dependency=E:\home\rst_prj\scratchpad\target\debug\deps` (exit code: 101)
```

gcc runs from the command line

```
$ gcc --version
gcc.exe (Rev5, Built by MSYS2 project) 5.3.0
Copyright (C) 2015 Free Software Foundation, Inc.
```

Both stable and nightly seem to be affected the same way.

Since there may be something funky in my path...

```
$ echo $PATH
/mingw64/bin:/usr/local/bin:/usr/bin:/bin:/c/Windows/System32:/c/Windows:/c/Windows/System32/Wbem:/c/Windows/System32/WindowsPowerShell/v1.0/:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
```