LLVM mangler doesn't mangle AVX instructions

The LLVM mangler does not currently transform AVX instructions on x86-64 platforms, due to a missing #include. Also, it is significantly more complicated than necessary, due to the file into sections (not needed anymore), and is sensitive to the details of the whitespace in the assembly.

I have attached a modified mangler that I believe to be simpler and more robust. I have not tested it, though, as I do not have a recent enough version of LLVM on my machine.

I am marking this as `Runtime crash' because that is what would happen if the unchanged AVX instructions made their way into the executable.

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (LLVM)
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