Update mipsel-unknown-linux-musl too.

ci/docker/mipsel-unknown-linux-musl/Dockerfile

@@ -6,19 +6,19 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 RUN mkdir /toolchain
 
-# Linux kernel version: 4.14.151
-# See build_dir/target-mipsel_mips32_musl/linux-brcm47xx_generic/linux-4.14.151
+# Linux kernel version: 5.4.154
+# See build_dir/target-mipsel_mips32_musl/linux-brcm47xx_generic/linux-5.4.154
 # Musl version: 1.1.24
-# See staging_dir/toolchain-mipsel_mips32_gcc-7.4.0_musl/info.mk
-RUN curl --retry 5 -L https://downloads.openwrt.org/releases/19.07.0-rc1/targets/brcm47xx/generic/openwrt-sdk-19.07.0-rc1-brcm47xx-generic_gcc-7.4.0_musl.Linux-x86_64.tar.xz | \
+# See staging_dir/toolchain-mipsel_mips32_gcc-8.4.0_musl/info.mk
+RUN curl --retry 5 -L https://downloads.openwrt.org/releases/21.02.1/targets/bcm47xx/generic/openwrt-sdk-21.02.1-bcm47xx-generic_gcc-8.4.0_musl.Linux-x86_64.tar.xz | \
     tar xJf - -C /toolchain --strip-components=1
 
 # See https://lkml.org/lkml/2014/3/14/269
 COPY sysinfo_guard.patch /toolchain
-RUN patch /toolchain/staging_dir/toolchain-mipsel_mips32_gcc-7.4.0_musl/include/linux/kernel.h </toolchain/sysinfo_guard.patch
+RUN patch /toolchain/staging_dir/toolchain-mipsel_mips32_gcc-8.4.0_musl/include/linux/kernel.h </toolchain/sysinfo_guard.patch
 
-ENV PATH=$PATH:/rust/bin:/toolchain/staging_dir/toolchain-mipsel_mips32_gcc-7.4.0_musl/bin \
+ENV PATH=$PATH:/rust/bin:/toolchain/staging_dir/toolchain-mipsel_mips32_gcc-8.4.0_musl/bin \
     STAGING_DIR=/toolchain/staging_dir \
     CC_mipsel_unknown_linux_musl=mipsel-openwrt-linux-musl-gcc \
     CARGO_TARGET_MIPSEL_UNKNOWN_LINUX_MUSL_LINKER=mipsel-openwrt-linux-musl-gcc \
-    CARGO_TARGET_MIPSEL_UNKNOWN_LINUX_MUSL_RUNNER="qemu-mipsel -L /toolchain/staging_dir/toolchain-mipsel_mips32_gcc-7.4.0_musl"
+    CARGO_TARGET_MIPSEL_UNKNOWN_LINUX_MUSL_RUNNER="qemu-mipsel -L /toolchain/staging_dir/toolchain-mipsel_mips32_gcc-8.4.0_musl"