ensure _Unwind_Backtrace to actually be available

[sergiud]

No description provided.

[codecov-commenter]

Codecov Report

Merging #767 (50d7e3f) into master (9dc1107) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #767   +/-   ##
=======================================
  Coverage   72.63%   72.63%           
=======================================
  Files          17       17           
  Lines        3241     3241           
=======================================
  Hits         2354     2354           
  Misses        887      887           

Impacted Files	Coverage Δ
src/stacktrace_unwind-inl.h	92.85% <ø> (ø)
src/utilities.h	100.00% <ø> (ø)

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