utility.cpp: fix lgamma_r for Darwin

[barracuda156]

No description provided.

[barracuda156]

Otherwise this happens:

/opt/local/bin/g++-mp-13 -std=gnu++17 -I"/opt/local/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -DR_BUILD -I'/opt/local/Library/Frameworks/R.framework/Versions/4.4/Resources/library/Rcpp/include' -I'/opt/local/Library/Frameworks/R.framework/Versions/4.4/Resources/library/RcppEigen/include' -isystem/opt/local/include/LegacySupport -I/opt/local/include    -fPIC  -pipe -Os -arch ppc   -c utility.cpp -o utility.o
utility.cpp: In function 'double ranger::mylgamma(double)':
utility.cpp:697:10: error: 'lgamma_r' was not declared in this scope; did you mean 'lgammal'?
  697 |   return(lgamma_r(x, &gamma_sign));
      |          ^~~~~~~~
      |          lgammal
make: *** [utility.o] Error 1
ERROR: compilation failed for package ‘ranger’