print_memory_usage() reports bogus values for virtual memory usage

[fredrik-johansson]

On Linux:

$ build/examples/pi 1000000
precision = 3321933 bits... cpu/wall(s): 0.227 0.228
virt/peak/rss/peak: 20.0 TB / 20.0 TB /  131 MB /  131 MB
[3.14159265358979323846{...999959 digits...}42209010610577945815 +/- 1.38e-1000000]

This seems to have broken with recent edits to profiler.c.