Assembly target architecture support

[ForNeVeR]

In scope of #132, we want to introduce proper support of assembly target architectures:

• 32b architecture set should target x86 and ARM32,
• 64b architecture set should target x86_64 and ARM64,
• all the others should still support any CPU (same as before).

If it's impossible to emit same assembly for x64 and ARM32, or for x86_64 and ARM64, we should divide them further, thus removing the concept of an architecture set and introducing more standard concept of an architecture.

When implementing, make sure to eliminate every instance of substring #353 in compiler's code and documentation.