Revert "Merge pull request #6807 from alblue/SR-1676"

[alblue]

This reverts commit c85cbe5, reversing
changes made to 5d293ab.

Build fails on Ubuntu 14.04 with 'unsupported compiler'. Unclear why this fails when this code builds as part of libdispatch project already, and it appears to be using the correct compiler.

In file included from allocator.c:21:
In file included from ./internal.h:616:
./shims.h:252:2: error: unsupported compiler
#error unsupported compiler
^

[rintaro]

Toolchain build uses "just built" clang in LLVM build directory.
https://github.com/apple/swift/blob/master/utils/build-script-impl#L2470-L2471
not /usr/bin/clang.

[rintaro]

@swift-ci Please smoke test

[alblue]

So it looks like the build fails when running against a 3.6 compiler, but works against a 3.8 compiler:

root@2f406866081b:/tmp# clang-3.8 foo.c
root@2f406866081b:/tmp# clang-3.6 foo.c
In file included from foo.c:1:
./foo.h:8:2: error: unsupported compiler
#error unsupported compiler
^
1 error generated.

That would be consistent with the libdispatch using its own version, so I'll see if I can replicate that. Thanks!

[alblue]

I've managed to reproduce the error seen here, and have something that works to build it. I'll do some more testing and then push an updated patch later.

[alblue]

Thanks