[c++] Set warnings-as-errors to be off by default

[jp-dark]

Issue and/or context:
Warnings as errors are useful for developers/CI, but cause unnecessary friction for users. Turn them off by default. See issue #3087.

Changes:

• Set TILEDBSOMA_ENABLE_WERROR to be OFF by default.
• Allow user to set TILEDBSOMA_ENABLE_WERROR as an environment variable. This can be overridden by a user provided value.
• Fix CMake code checking if TILEDBSOMA_ENABLE_WERROR is OFF.
• Update the build script to take werror as an argument.
• Explicitly set werror=true for CI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.30%. Comparing base (46bf2ec) to head (a8dfa1b).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3159      +/-   ##
==========================================
+ Coverage   82.92%   83.30%   +0.38%     
==========================================
  Files          50       51       +1     
  Lines        5236     5458     +222     
==========================================
+ Hits         4342     4547     +205     
- Misses        894      911      +17     

Flag	Coverage Δ
python	83.30% <ø> (+0.38%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
python_api	83.30% <100.00%> (+0.38%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[johnkerl]

Unless I'm missing it we need some way to be sure this flag is always set for devleopers. Maybe some env-var check and we can be sure to all set it in our shell .rc files ...

[johnkerl]

🔥