Added C++ support

[vnitu02]

Summary of this Pull Request (PR)

• Added a posix abstraction layer over COS
• Enabled the malloc/free real implementation in musl
• Fixed the vas_frontier bug in cos_pgtbl_intern_expandwith()
• Added the C++ library

Intent for your PR

Choose one (Mandatory):

• [ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [x] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

@gparmer @ryuxin @phanikishoreg

Code Quality

As part of this pull request, I've considered the following:

Style:

• [ ] Comments adhere to the Style Guide (SG)
• [ ] Spacing adhere's to the SG
• [ ] Naming adhere's to the SG
• [ ] All other aspects of the SG are adhered to, or exceptions are justified in this pull request

Code Craftsmanship:

• [ ] I've made an attempt to remove all redundant code
• [ ] I've considered ways in which my changes might impact existing code, and cleaned it up
• [ ] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [ ] I've commented appropriately where code is tricky
• [ ] I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

-unit_cxx with tests for C++ library

[gparmer]

@ryuxin since some of this code was initially his.

[gparmer]

I can't see what the modification to the ps library is, but it says that there is a one-line change. It is unlikely that is desirable.

[gparmer]

I'm closing this for now so that your next PR will be a clean submit. Thanks @Others for the thorough comments here.

@RobertGiff you're going to be looking into musl integration with rumpkernels, so it might be useful to see how the posix library works here, and how to define new "system calls".

[phanikishoreg]

We'll probably need a section in CSG for C++ coding style if we see ourselves writing C++ code in Composite in the future. ;)