docker: Upgrade GCC to 10.3-2021.07

Upgrade to the current latest version of GNU Arm Embedded,
gcc-arm-none-eabi-10.3-2021.07. This brings along fixes to v8-M targets
and better Cortex-M55 support.

docker_images/mbed-os-env/Dockerfile

@@ -63,16 +63,16 @@ RUN set -x \
 WORKDIR /opt/mbed-os-toolchain
 RUN set -x \
     && [ "$(uname -m)" = "aarch64" ] && \
-        TARBALL="gcc-arm-none-eabi-9-2019-q4-major-aarch64-linux.tar.bz2" || \
-        TARBALL="gcc-arm-none-eabi-9-2019-q4-major-x86_64-linux.tar.bz2" \
-    && wget -q https://developer.arm.com/-/media/Files/downloads/gnu-rm/9-2019q4/RC2.1/${TARBALL} \
+        TARBALL="gcc-arm-none-eabi-10.3-2021.07-aarch64-linux.tar.bz2" || \
+        TARBALL="gcc-arm-none-eabi-10.3-2021.07-x86_64-linux.tar.bz2" \
+    && wget -q https://developer.arm.com/-/media/Files/downloads/gnu-rm/10.3-2021.07/${TARBALL} \
     && tar -xjf ${TARBALL} \
     && rm ${TARBALL} \
     && : # last line
 
 # ------------------------------------------------------------------------------
 # Configure environment variables
-ENV MBED_GCC_ARM_PATH=/opt/mbed-os-toolchain/gcc-arm-none-eabi-9-2019-q4-major/bin/
+ENV MBED_GCC_ARM_PATH=/opt/mbed-os-toolchain/gcc-arm-none-eabi-10.3-2021.07/bin/
 ENV PATH="${PATH}:${MBED_GCC_ARM_PATH}"
 
 # ------------------------------------------------------------------------------