Fix host OS detection for darwin-specific linker flag

configure.ac

@@ -274,9 +274,11 @@ AC_CHECK_FUNCS([strsignal posix_fallocate sysconf])
 
 # This is needed if bzip2 is a static library, and the Nix libraries
 # are dynamic.
-if test "$(uname)" = "Darwin"; then
+case "${host_os}" in
+  darwin*)
     LDFLAGS="-all_load $LDFLAGS"
-fi
+    ;;
+esac
 
 
 AC_ARG_WITH(sandbox-shell, AS_HELP_STRING([--with-sandbox-shell=PATH],[path of a statically-linked shell to use as /bin/sh in sandboxes]),