Enabled heap_and_stack test for baremetal.
Added a test to check that global variables are initialised.
In mbed_sdk_boot:
- Added initialisation for mbed_stack_isr_start/size and mbed_heap_start/size for all toolchains.
- ARM toolchain:
- Added call to mbed_toolchain_init() to initialise global variables.
- Moved microlib initialisation code from mbed_retarget.cpp to mbed_sdk_boot.c.
- IAR toolchain: there is no equivalent to a software init hook that can be called. __low_level_init() was used but since this function is called before RAM initialisation, it cannot be used to initialize global variables. Defined a new __mbed_init() function called from IAR startup file instead.
If the fault handler was hit before the stdio console was used and
initialised, the initialisation code caused a "mutex in ISR" trap,
stopping the register dump from happening.
Temporarily set the `error_in_progress` flag at the top of the fault
handler, and restore it before calling `mbed_error`. Take the
opportunity to suppress fault dumps on recursive crashes, much as is
done inside `mbed_error`.