Use C++ features and headers in C++ code instead of C

[AZero13]

We don’t need to use integers as booleans or the C standard headers when we have the C++ standard headers and booleans

[supahero1]

lib/csu/tests/cxx_constructors.cc:56 1 substituted for false?

[bsdimp]

Too many changes in this to effectively review. Please split it up into logical changes.

[bsdimp]

This pull request is too wide-ranging. The changes are likely be good, but it's impossible to land as is. Please create a new pull request per directory as there are different reviewers needed for different parts of the tree. Some of the changes add std:: (which is likely right, but not mentioned) and noexcept (which may or may not be right, I didn't study the code to know). at the very least, this information should be reflected i the commit messages. Thanks.