Re-organize intrinsic-test to enable seamless addition of behaviour testing for more architectures

[madhav-madhusoodanan]

Updates so far

1. Moved the ARM-specific testing to the arm module, exposing only a test function at src/main.rs
2. Created a SupportedArchitectureTest trait that has been implemented for arm and should be implemented for other architectures too. Allows us to expose functionality like building C/Rust test files and comparing outputs.
3. Moved common functionality (CLI parsing, create files, compilations, compare outputs) into the common module for reuse by other architectures too.
4. Implemented a match block for selection of architectures using the target CLI variable.

Reasoning

1. The Intrinsic type may be specific to architectures, hence the implementation of a trait helps us to abstract the usage of such data types within the architecture-specific module

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[Amanieu]

The module should be called arm rather than aarch.

[Amanieu]

@JamieCunliffe feel free to have a look at this since you are the original author of intrinsic-test. This is part of a GSoC project to extend intrinsic-test to other architectures.

[madhav-madhusoodanan]

Are we using the --a32 flag in the CLI of intrinsic-test anywhere? I was unable to find its usage.
Would it be alright if I remove it, or is there some reasoning that I may be missing?

[Amanieu]

--a32 is not currently tested in CI, but it is used for 32-bit ARM targets (arm* and thumb*). Some ARM intrinsics are only available on 64-bit ARM targets and this flag skips those.