Do not clobber the CMAKE_C_FLAGS value as part of the OSAL build.
Instead, use target_compile_options and target_include_directories
as needed to set the compile options for specific targets.

This also creates a separate CMakeLists.txt file for each OS/BSP
implementation library rather than using aux_source_directory.
Each implementation-specific build can then set any additional
options as required for that platform.

Note that any entity needing to compile/link with OSAL should
now obtain the requisite compile flags and directories by querying
the INTERFACE_COMPILE_DEFINITIONS and INTERFACE_INCLUDE_DIRECTORIES
properties on the osal library target.

Refactor the OSAL BSP code so that a single BSP implementation
can work for both normal applications as well as unit tests.

This intoduces a new bsp implementation abstraction layer akin
to the low level OS implementation layer.  This handles dealing
with bootloader/command line arguments, and debug console
manipluation.

Build the full suite of OSAL coverage tests as part of
the normal build when ENABLE_UNIT_TESTS is true.

This will use the same target OSAL BSP to execute the tests
as is used for the FSW.

This ensures that the return value of the write() call is checked,
and avoids a potential compiler warning.  There is still no recourse if
the write call fails, but it can retry if it was short.

Avoids calling write() if length is zero.