Add guards to user configurable macro definitions

[mborland]

Closes: #1137

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.71%. Comparing base (52be1ad) to head (7d85d73).

Additional details and impacted files

[](https://app.codecov.io/gh/boostorg/math/pull/1138?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ```diff @@ Coverage Diff @@ ## develop #1138 +/- ## ======================================== Coverage 93.71% 93.71% ======================================== Files 771 772 +1 Lines 61166 61168 +2 ======================================== + Hits 57321 57323 +2 Misses 3845 3845 ``` | [Files](https://app.codecov.io/gh/boostorg/math/pull/1138?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) | Coverage Δ | | |---|---|---| | [test/git\_issue\_1137.cpp](https://app.codecov.io/gh/boostorg/math/pull/1138?src=pr&el=tree&filepath=test%2Fgit_issue_1137.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-dGVzdC9naXRfaXNzdWVfMTEzNy5jcHA=) | `100.00% <100.00%> (ø)` | | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/boostorg/math/pull/1138?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/boostorg/math/pull/1138?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Last update [52be1ad...7d85d73](https://app.codecov.io/gh/boostorg/math/pull/1138?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg).