Replace Maddr with uintptr_t

[harrysarson]

Problem

• make gives a fair few warnings: warning: cast from pointer to integer of different size.
• These are all due to casts from void * (32 bit) to Maddr (64 bit).

Solutions

• This cast is safe (as the number of bits are increasing) so we could turn off the warning.
• However, there is a type designed for storing pointers as an int: uintptr_t (https://en.cppreference.com/w/c/types/integer).
• The Maddr is only using in mmalloc.c. Unless there is some deeper perpose behind Maddr that I am missing we seem to have "reinvented the wheel" and we could simplify the code base as well as removing these compiler warnings by using uintptr_t here.