ArgoDSM reserved VM possibly too large under MEMFD

It appears that when using MEMFD, the default size of the ArgoDSM VM is too large for "some" systems.

When inspecting the memory mappings of a running ArgoDSM process using SHM, the default value of ARGO_END appears too large and intrudes on the mapping of the heap among other things.

5562b64b2000-5562b64b3000 rw-p 0009c000 103:08 8528772                   /home/sven/git/argodsm/build/bin/mpi/barrierTests
5562b6d06000-5562b7108000 rw-p 00000000 00:00 0                          [heap]
7fe8a0000000-7fe8a0021000 rw-p 00000000 00:00 0

As a result the initial anonymous mapping below fails using MEMFD:

argodsm/src/virtual_memory/memfd.cpp

Line 58 in 605645a

    
           start_addr = ::mmap(static_cast<void*>(ARGO_START), ARGO_SIZE, PROT_NONE, flags, -1, 0);

This mapping succeeds on my system if ARGO_END is set to for example 0x500000000000l (Or 0x550000000000l, while 0x560000000000l occasionally fails). I have observed the same behavior (approximate mapping of the heap and failure to map using MEMFD) on other Debian-based machines.

Having been occupied with other projects for a while I seem to have forgotten there was already a related issue open. Closing this and referring to #124 instead.