Add macos-compatible nproc alternative

Without this we were running `make -j` on macos which is a minor fork
bomb.  Also adds a workaround in case that doesn't work either to fall
back to just -j1.

utils/static-bundle.sh

@@ -63,7 +63,7 @@ cmake -G 'Unix Makefiles' \
     "$@" \
     "$projdir"
 
-make -j${JOBS:-$(nproc)} VERBOSE=1 session-util
+make -j${JOBS:-$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 1)} VERBOSE=1 session-util
 
 if [ -z "$archive" ]; then
     exit 0