gmic: fix build on aarch64-darwin

pkgs/tools/graphics/gmic/default.nix

···
 
     # CMake build files were moved to subdirectory.
     mv resources/CMakeLists.txt resources/cmake .
+  '' + lib.optionalString stdenv.isDarwin ''
+    substituteInPlace CMakeLists.txt \
+      --replace "LD_LIBRARY_PATH" "DYLD_LIBRARY_PATH"
   '';
 
   passthru = {