lib: newlib: Add minimum required heap size config

This commit adds a new `CONFIG_NEWLIB_MIN_REQUIRED_HEAP_SIZE` config
that allows user to specify the minimum required heap size for the
newlib heap, and makes `malloc_prepare` validate that the memory space
available for the newlib heap is greater than this value.

The default minimum required heap size values were empiricially
determined, so as to allow the basic standard C functions such as
`printf` and `scanf` to work properly.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
2 files changed