Header Guards for C++ applications to call CFE, OSAL, PSP

[irowebbn]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I reviewed the cFS README.md file to see if the feature is in the major future work.
• I performed a cursory search to see if the feature request is relevant, not redundant, nor in conflict with other tickets.

Describe the solution you'd like
Wrap all public headers in CFE, OSAL, and PSP in hedaer guards that allow inclusion from C++ translation units:

#ifdef __cplusplus
extern "C" {
#endif

<content>

#ifdef __cplusplus
}
#endif

Describe alternatives you've considered
The alternative is to wrap the #includes in the calling apps with the header guards.

Additional context

• https://lists.nasa.gov/archives/list/[email protected]/thread/HMXU7ORGRU5ZWPAXIBNCI2MEDL5WL6RW/
• Guidelines for implementing apps in C++ #659
• https://lists.nasa.gov/archives/list/[email protected]/thread/OANSPI46GVMPNNNSB467P5LD23F274GO/
• https://lists.nasa.gov/archives/list/[email protected]/thread/3BRMUGGE2TOLGKIP6NIQNZV4UWTJIUAF/

Requester Info
Isaac Rowe, NASA JSC, Jacobs Technology