Add support for compile time setting of debug stream

[jeromekelleher]

Proposal to help with R integration in #3363

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.76%. Comparing base (b7fd993) to head (bef1c50).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3364   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          29       29           
  Lines       31292    31292           
  Branches     5738     5738           
=======================================
  Hits        28089    28089           
  Misses       1794     1794           
  Partials     1409     1409           

Flag	Coverage Δ
c-tests	86.77% <100.00%> (ø)
lwt-tests	80.38% <ø> (ø)
python-c-tests	87.12% <ø> (ø)
python-tests	98.85% <ø> (ø)
python-tests-no-jit	33.51% <ø> (ø)
python-tests-numpy1	50.28% <ø> (ø)

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Files with missing lines	Coverage Δ
c/tskit/core.c	95.63% <100.00%> (ø)
c/tskit/core.h	100.00% <ø> (ø)

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