Check all tier 1 targets in PR CI

Author: ChrisDenton

src/ci/docker/host-x86_64/mingw-check/Dockerfile

@@ -46,6 +46,8 @@ ENV SCRIPT python3 ../x.py --stage 2 test src/tools/expand-yaml-anchors && \
            python3 ../x.py build --stage 0 src/tools/build-manifest && \
            python3 ../x.py test --stage 0 src/tools/compiletest && \
            python3 ../x.py test --stage 0 core alloc std test proc_macro && \
+           # check all tier 1 targets
+           python3 ../x.py check --stage 0 --target=aarch64-unknown-linux-gnu,i686-pc-windows-gnu,i686-pc-windows-msvc,i686-unknown-linux-gnu,x86_64-apple-darwin,x86_64-pc-windows-gnu,x86_64-pc-windows-msvc,x86_64-unknown-linux-gnu && \
            # Build both public and internal documentation.
            RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc --stage 0 library && \
            mkdir -p /checkout/obj/staging/doc && \