I added the process for Cortex-A in mbed_application.c because this process was for only Cortex-M.
Also I enabled the macro of MBED_APPLICATION_SUPPORT for Cortex-A.
A define which expands to more defines is not portable across all
compilers and GCC warns about this. Restructure this so the behavior
is defined. This fixes the GCC warning:
"this use of "defined" may not be portable"