- By default, Mbed OS build tools use standard C library for all supported toolchains.
   It is possible to use smaller C libraries by overriding the "target.default_lib" option
   with "small". This option is only currently supported for the GCC_ARM toolchain.
   This override config option is now extended in the build tool for ARM toolchain.
 - Add configuration option to specify libraries supported for each toolchain per targets.
 - Move __aeabi_assert function from rtos to retarget code so it’s available for bare metal.
 - Use 2 memory region model for ARM toolchain scatter file for the following targets:
   NUCLEO_F207ZG, STM32F411xE, STM32F429xI, NUCLEO_L073RZ, STM32F303xE
 - Add a warning message in the build tools to deprecate uARM toolchain.
 - NewLib-Nano C library is not supporting floating-point and printf with %hhd,%hhu,%hhX,%lld,%llu,%llX
   format specifier so skipping those green tea test cases.

The ARMC6 compiler inadvertently introduces the `_scanf_mbtowc` symbol
to the build. The commit provides a weak definition of the symbol to
satisfy the linker whenever the symbol is included. This affects ARM
Compiler 6 version 6.12 and earlier.

The compiler error was previously observed when the MICROLIB library is
used with the uARM toolchain. However, the weak definition was put in
`mbed-os/rtos` which is not included when the bare metal profile is used.