[libc] Update v7malloc to use __dprintf instead of fprintf

[ghaerr]

Malloc/v7malloc doesn't drag in stdio anymore, uses small __dprintf for simple formatting. No other functional changes with v7malloc, it isn't normally used by applications.

Malloc debug output through __dprintf now goes to console automatically, not stderr.

Also retabs v7malloc.c, see second commit for non retabbing changes.

This is in preparation for using v7malloc's arena allocator for upcoming 64K near heap allocator for the 8086 toolchain.