Use separate source files and CMake-based source selection
to configure OSAL features, rather than using the C preprocessor.

This commit covers the OSAL coverage test.  This had been using
inclusion of a C file to allow access to static functions/variables.
This updates all UT code to correspond with the FSW code changes.
All "static" helper functions become non-static so unit test can
invoke directly.  Prototype is in a private header, so
the functions are still not exposed in the API.

Permissive mode is required for testing on POSIX when
running as a normal (non-root) user.

Fix #285, Refactor OSAL to avoid inclusion of C files

The "include()" cmake function only read the first file when passed a list.
Adding a foreach loop supports allowing a list of files which is useful
for adding and override/addendum file to a base config.

Definitions within osconfig.h are referenced by doxygen
in other source code files, so this should also include
doxygen-formatted descriptions of each macro defined by
this template file.