cmsis-freertos-fri: Add support for building with ARMClang

This commit adds support for building the project with the Arm Compiler
for Embedded toolchain. The build.sh file is also updated to allow a
user to specify which toolchain to build with. In addition, the relevant
documentation has been updated to reflect these changes.

Signed-off-by: Chuyue Luo <Chuyue.Luo@arm.com>