Add intrinsic support for atomic store and load.

[lucteo]

Add intrinsic support for atomic store and load.
Also add void intrinsic type.

[codecov]

Codecov Report

Attention: Patch coverage is 38.09524% with 39 lines in your changes missing coverage. Please review.

Project coverage is 88.32%. Comparing base (734e7be) to head (b67d41f).

Files with missing lines	Patch %	Lines
Sources/FrontEnd/BuiltinFunction.swift	22.22%	21 Missing ⚠️
Sources/FrontEnd/NativeInstruction.swift	50.00%	12 Missing ⚠️
Sources/FrontEnd/Types/BuiltinType.swift	50.00%	2 Missing ⚠️
Sources/CodeGen/LLVM/ConcreteTypeLayout.swift	50.00%	1 Missing ⚠️
Sources/CodeGen/LLVM/TypeLowering.swift	50.00%	1 Missing ⚠️
Sources/IR/Mangling/Demangler.swift	50.00%	1 Missing ⚠️
Sources/IR/Mangling/Mangler.swift	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1628      +/-   ##
==========================================
- Coverage   88.44%   88.32%   -0.12%     
==========================================
  Files         381      381              
  Lines       30359    30422      +63     
==========================================
+ Hits        26851    26871      +20     
- Misses       3508     3551      +43     

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