Rollup merge of #52465 - sekineh:add-ci-thumb, r=alexcrichton

Add CI test harness for `thumb*` targets. [IRR-2018-embedded]

This pull request will do the following (rather trivial) changes:
- Fix #52163. In other words, we enabled `./x.py test src/test/run-make` for `no_std` targets.
- Modify `dist-various-1` Dockerfile.
  - CI now performs `run-make` test run on the targets below:
    - `thumbv6m-none-eabi`
    - `thumbv7m-none-eabi`
    - `thumbv7em-none-eabi`
    - `thumbv7em-none-eabihf`.
- ~~Add `thumb-none` Dockerfile.~~
  - ~~Initially, `thumbv7m-none-eabi`, `thumbv7em-none-eabi` and `thumbv7em-none-eabihf` are included as the tested target. `thumbv6m-none-eabi` is disabled for now because LLVM support is not certain.~~
- ~~Add `thumb-none` to .travis.yml~~

Note:
- `run-make` tests are not implemented yet. This PR is test harness only.

The amount of change is very small, but I'd like to open the pull request while the change is trivial.
Because I'm not very used to pull request process, I want to make a small progress first.  This PR will be a foundation for later additions.

src/bootstrap/test.rs

@@ -966,7 +966,9 @@ impl Step for Compiletest {
             builder.ensure(compile::Rustc { compiler, target });
         }
 
-        builder.ensure(compile::Test { compiler, target });
+        if builder.no_std(target) != Some(true) {
+            builder.ensure(compile::Test { compiler, target });
+        }
         builder.ensure(native::TestHelpers { target });
         builder.ensure(RemoteCopyLibs { compiler, target });
 

src/ci/docker/dist-various-1/Dockerfile

@@ -80,6 +80,11 @@ RUN \
   echo "# a" >> /usr/local/mips-linux-musl/bin/mips-openwrt-linux-musl-wrapper.sh && \
   echo "# b" >> /usr/local/mipsel-linux-musl/bin/mipsel-openwrt-linux-musl-wrapper.sh
 
+ENV RUN_MAKE_TARGETS=thumbv6m-none-eabi
+ENV RUN_MAKE_TARGETS=$RUN_MAKE_TARGETS,thumbv7m-none-eabi
+ENV RUN_MAKE_TARGETS=$RUN_MAKE_TARGETS,thumbv7em-none-eabi
+ENV RUN_MAKE_TARGETS=$RUN_MAKE_TARGETS,thumbv7em-none-eabihf
+
 ENV TARGETS=asmjs-unknown-emscripten
 ENV TARGETS=$TARGETS,wasm32-unknown-emscripten
 ENV TARGETS=$TARGETS,x86_64-rumprun-netbsd
@@ -120,7 +125,9 @@ ENV RUST_CONFIGURE_ARGS \
       --enable-emscripten \
       --disable-docs
 
-ENV SCRIPT python2.7 ../x.py dist --target $TARGETS
+ENV SCRIPT \ 
+      python2.7 ../x.py test --target $RUN_MAKE_TARGETS src/test/run-make && \
+      python2.7 ../x.py dist --target $TARGETS
 
 # sccache
 COPY scripts/sccache.sh /scripts/