Move llvm-profdata build into MK_LLVM_COV block

Move llvm-profdata build into MK_LLVM_COV block

llvm-profdata is used with llvm-cov for code coverage (although llvm-cov
can also operate independently in a gcov-compatible mode).
Although llvm-profdata can be used independently of llvm-cov it makes
sense to group these under one option.

Also handle these in OptionalObsoleteFiles.inc while here.

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