[memprof] Move the meminfo block struct to MemProfData.inc.

The definition of the MemInfoBlock is shared between the memprof
compiler-rt runtime and llvm/lib/ProfileData/. This change removes the
memprof_meminfoblock header and moves the struct to the shared include
file. To enable this sharing, the Print method is moved to the
memprof_allocator (the only place it is used) and the remaining uses are
updated to refer to the MemInfoBlock defined in the MemProfData.inc
file.

Also a couple of other minor changes which improve usability of the
types in MemProfData.inc.
* Update the PACKED macro to handle commas.
* Add constructors and equality operators.
* Don't initialize the buildid field.

Differential Revision: https://reviews.llvm.org/D116780