ci: add support for loongarch64-unknown-linux-gnu

(backport <#4000>)
(cherry picked from commit 705bb12)

Author: heiher

.github/workflows/full_ci.yml

@@ -171,6 +171,7 @@ jobs:
           - arm-unknown-linux-musleabihf
           - i686-linux-android
           - i686-unknown-linux-musl
+          - loongarch64-unknown-linux-gnu
           - powerpc-unknown-linux-gnu
           - powerpc64-unknown-linux-gnu
           - powerpc64le-unknown-linux-gnu

ci/docker/loongarch64-unknown-linux-gnu/Dockerfile

@@ -0,0 +1,12 @@
+FROM ubuntu:24.04
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        gcc libc6-dev qemu-user ca-certificates \
+        gcc-14-loongarch64-linux-gnu libc6-dev-loong64-cross \
+        linux-headers-generic
+
+ENV CARGO_TARGET_LOONGARCH64_UNKNOWN_LINUX_GNU_LINKER=loongarch64-linux-gnu-gcc-14 \
+    CARGO_TARGET_LOONGARCH64_UNKNOWN_LINUX_GNU_RUNNER="qemu-loongarch64 -L /usr/loongarch64-linux-gnu" \
+    CC_loongarch64_unknown_linux_gnu=loongarch64-linux-gnu-gcc-14 \
+    CFLAGS_loongarch64_unknown_linux_gnu="-mabi=lp64d -fPIC" \
+    PATH=$PATH:/rust/bin