Added simple stats tracking memory usage

[mjp41]

These statistics can be maintained with effectively zero cost to
realistic applications. They do not track the precise amount of
memory used, but are an over-approximation.

[mjp41]

This is not quite finished as the API is not surfaced properly. After suggestions for what to do.

• Expose a struct, and return that
• Expose a struct, and fill in a reference to that
• Two function one to return peak, and one to return current usage

The C++ code just returns a pair, but I guess we want a C function for broader use.

[mjp41]

Addresses #240

[mjp41]

Output from the new unit test:

> Debug\func-memory_usage-1.exe
Memory Usages Changed to (1130560, 1130560)
Memory Usages Changed to (2179136, 2179136)
Memory Usages Changed to (3227712, 3227712)
Memory Usages Changed to (4276288, 4276288)
Memory Usages Changed to (5324864, 5324864)
Init complete!
Memory Usages Changed to (4276288, 5324864)
Phase 0 remove complete!
Memory Usages Changed to (5324864, 5324864)
Memory Usages Changed to (6373440, 6373440)
Phase 0 add complete!
Memory Usages Changed to (5324864, 6373440)
Phase 1 remove complete!
Memory Usages Changed to (6373440, 6373440)
Memory Usages Changed to (7422016, 7422016)
Phase 1 add complete!
Memory Usages Changed to (6373440, 7422016)
Phase 2 remove complete!
Memory Usages Changed to (7422016, 7422016)
Memory Usages Changed to (8470592, 8470592)
Phase 2 add complete!
Memory Usages Changed to (7422016, 8470592)
Phase 3 remove complete!
Memory Usages Changed to (8470592, 8470592)
Memory Usages Changed to (9519168, 9519168)
Phase 3 add complete!
Memory Usages Changed to (8470592, 9519168)
Phase 4 remove complete!
Memory Usages Changed to (9519168, 9519168)
Memory Usages Changed to (10567744, 10567744)
Phase 4 add complete!
Memory Usages Changed to (9519168, 10567744)
Phase 5 remove complete!
Memory Usages Changed to (10567744, 10567744)
Memory Usages Changed to (11616320, 11616320)
Phase 5 add complete!
Memory Usages Changed to (10567744, 11616320)
Phase 6 remove complete!
Memory Usages Changed to (11616320, 11616320)
Memory Usages Changed to (12664896, 12664896)
Phase 6 add complete!
Memory Usages Changed to (11616320, 12664896)
Phase 7 remove complete!
Memory Usages Changed to (12664896, 12664896)
Memory Usages Changed to (13713472, 13713472)
Phase 7 add complete!
Memory Usages Changed to (12664896, 13713472)
Phase 8 remove complete!
Memory Usages Changed to (13713472, 13713472)
Memory Usages Changed to (14762048, 14762048)
Phase 8 add complete!
Memory Usages Changed to (13713472, 14762048)
Phase 9 remove complete!
Memory Usages Changed to (14762048, 14762048)
Memory Usages Changed to (15810624, 15810624)
Phase 9 add complete!
Memory Usages Changed to (14762048, 15810624)
Memory Usages Changed to (13713472, 15810624)
Phase 0 remove complete!
Memory Usages Changed to (14762048, 15810624)
Phase 0 add complete!
Memory Usages Changed to (13713472, 15810624)
Memory Usages Changed to (12664896, 15810624)
Phase 1 remove complete!
Memory Usages Changed to (13713472, 15810624)
Phase 1 add complete!
Memory Usages Changed to (12664896, 15810624)
Memory Usages Changed to (11616320, 15810624)
Phase 2 remove complete!
Memory Usages Changed to (12664896, 15810624)
Phase 2 add complete!
Memory Usages Changed to (11616320, 15810624)
Memory Usages Changed to (10567744, 15810624)
Phase 3 remove complete!
Memory Usages Changed to (11616320, 15810624)
Phase 3 add complete!
Memory Usages Changed to (10567744, 15810624)
Memory Usages Changed to (9519168, 15810624)
Phase 4 remove complete!
Memory Usages Changed to (10567744, 15810624)
Phase 4 add complete!
Memory Usages Changed to (9519168, 15810624)
Memory Usages Changed to (8470592, 15810624)
Phase 5 remove complete!
Memory Usages Changed to (9519168, 15810624)
Phase 5 add complete!
Memory Usages Changed to (8470592, 15810624)
Memory Usages Changed to (7422016, 15810624)
Phase 6 remove complete!
Memory Usages Changed to (8470592, 15810624)
Phase 6 add complete!
Memory Usages Changed to (7422016, 15810624)
Memory Usages Changed to (6373440, 15810624)
Phase 7 remove complete!
Memory Usages Changed to (7422016, 15810624)
Phase 7 add complete!
Memory Usages Changed to (6373440, 15810624)
Memory Usages Changed to (5324864, 15810624)
Phase 8 remove complete!
Memory Usages Changed to (6373440, 15810624)
Phase 8 add complete!
Memory Usages Changed to (5324864, 15810624)
Memory Usages Changed to (4276288, 15810624)
Phase 9 remove complete!
Memory Usages Changed to (5324864, 15810624)
Phase 9 add complete!
Memory Usages Changed to (4276288, 15810624)
Memory Usages Changed to (3227712, 15810624)
Memory Usages Changed to (2179136, 15810624)
Teardown complete!

[mjp41]

I have incorporated your (@davidchisnall, @achamayou ) comments from #240 as best I can. Please check you feel this is a reasonable interpretation of your constraints and suggestions.

[achamayou]

That looks good to me, I think it meets both the requirements of the OE memory tests and those of users deploying Open Enclave-based services who want to monitor their memory usage.