libjxl fails on 10.4: fatal error: spawn.h: No such file or directory

[barracuda156]

[ 96%] Building CXX object tools/CMakeFiles/benchmark_xl.dir/benchmark/benchmark_utils.cc.o
cd /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/build/tools && /opt/local/bin/g++-mp-7 -DBENCHMARK_AVIF -DBENCHMARK_PNG -DBENCHMARK_WEBP -DFJXL_ENABLE_AVX512=0 -DHWY_DISABLED_TARGETS="(HWY_SSSE3|HWY_AVX3|HWY_AVX3_SPR|HWY_AVX3_ZEN4|HWY_SVE|HWY_SVE2|HWY_SVE_256|HWY_SVE2_128|HWY_RVV)" -DJXL_STATIC_DEFINE -D__DATE__=\"redacted\" -D__TIMESTAMP__=\"redacted\" -D__TIME__=\"redacted\" -I/opt/local/include/webp -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/libjxl-0.10.2 -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/build/lib/include -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/libjxl-0.10.2/lib/include -isystem /opt/local/include -pipe -Os -D_GLIBCXX_USE_CXX11_ABI=0 -fno-rtti -DNDEBUG -std=c++11 -arch ppc -mmacosx-version-min=10.4 -fPIE -funwind-tables -fno-omit-frame-pointer -Wno-builtin-macro-redefined -Wall -DHWY_SHARED_DEFINE -DAVIF_DLL -MD -MT tools/CMakeFiles/benchmark_xl.dir/benchmark/benchmark_utils.cc.o -MF CMakeFiles/benchmark_xl.dir/benchmark/benchmark_utils.cc.o.d -o CMakeFiles/benchmark_xl.dir/benchmark/benchmark_utils.cc.o -c /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/libjxl-0.10.2/tools/benchmark/benchmark_utils.cc
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_graphics_libjxl/libjxl/work/libjxl-0.10.2/tools/benchmark/benchmark_utils.cc:16:10: fatal error: spawn.h: No such file or directory
 #include <spawn.h>
          ^~~~~~~~~
compilation terminated.