Fix x86_64 code being produced for bare-metal LoongArch targets' compiler_builtins

Formerly the `loongarch*-*-none*` targets were added to the
`dist-various-2` CI job, but no corresponding toolchain was added along
with them. This meant the `compiler_builtins` for the targets were built
with the host toolchain.

As the other `dist-various` toolchains are mostly pre-built so far, to
avoid burdening them with crosstool-ng builds, simply move the two
bare-metal LoongArch targets to the `dist-loongarch64-linux` job which
has a ready-to-use LoongArch toolchain. With the proper CFLAGS applied
it is possible to build artifacts suitable for bare-metal. I verified
that the `compiler_builtins` objects are now correctly produced
regarding architecture and ABI, with the changes here applied.

Fixes rust-lang#125908.

cc @heiher

try-job: dist-loongarch64-linux
try-job: dist-various-2

Author: xen0n

src/ci/docker/host-x86_64/dist-loongarch64-linux/Dockerfile

@@ -23,12 +23,30 @@ ENV CC_loongarch64_unknown_linux_gnu=loongarch64-unknown-linux-gnu-gcc \
     AR_loongarch64_unknown_linux_gnu=loongarch64-unknown-linux-gnu-ar \
     CXX_loongarch64_unknown_linux_gnu=loongarch64-unknown-linux-gnu-g++
 
+# We re-use the Linux toolchain for bare-metal, because upstream bare-metal
+# target support for LoongArch is only available from GCC 14+.
+#
+# See: https://github.com/gcc-mirror/gcc/commit/976f4f9e4770
+ENV CC_loongarch64_unknown_none=loongarch64-unknown-linux-gnu-gcc \
+    AR_loongarch64_unknown_none=loongarch64-unknown-linux-gnu-ar \
+    CXX_loongarch64_unknown_none=loongarch64-unknown-linux-gnu-g++ \
+    CFLAGS_loongarch64_unknown_none="-ffreestanding -mabi=lp64d" \
+    CXXFLAGS_loongarch64_unknown_none="-ffreestanding -mabi=lp64d" \
+    CC_loongarch64_unknown_none_softfloat=loongarch64-unknown-linux-gnu-gcc \
+    AR_loongarch64_unknown_none_softfloat=loongarch64-unknown-linux-gnu-ar \
+    CXX_loongarch64_unknown_none_softfloat=loongarch64-unknown-linux-gnu-g++ \
+    CFLAGS_loongarch64_unknown_none_softfloat="-ffreestanding -mabi=lp64s -mfpu=none" \
+    CXXFLAGS_loongarch64_unknown_none_softfloat="-ffreestanding -mabi=lp64s -mfpu=none"
+
 ENV HOSTS=loongarch64-unknown-linux-gnu
+ENV TARGETS=$HOSTS
+ENV TARGETS=$TARGETS,loongarch64-unknown-none
+ENV TARGETS=$TARGETS,loongarch64-unknown-none-softfloat
 
 ENV RUST_CONFIGURE_ARGS \
       --enable-extended \
       --enable-full-tools \
       --enable-profiler \
       --disable-docs
 
-ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS
+ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $TARGETS

src/ci/docker/host-x86_64/dist-various-2/Dockerfile

@@ -121,8 +121,6 @@ ENV TARGETS=$TARGETS,armv7-unknown-linux-gnueabi
 ENV TARGETS=$TARGETS,armv7-unknown-linux-musleabi
 ENV TARGETS=$TARGETS,i686-unknown-freebsd
 ENV TARGETS=$TARGETS,x86_64-unknown-none
-ENV TARGETS=$TARGETS,loongarch64-unknown-none
-ENV TARGETS=$TARGETS,loongarch64-unknown-none-softfloat
 ENV TARGETS=$TARGETS,aarch64-unknown-uefi
 ENV TARGETS=$TARGETS,i686-unknown-uefi
 ENV TARGETS=$TARGETS,x86_64-unknown-uefi