xspawn: Use _Fork() if available

This completes the workaround for bfs_spawn() hanging on FreeBSD with
ASan enabled.

Link: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280318

1 files changed, 8 insertions, 0 deletions

diff --git a/build/has/_Fork.c b/build/has/_Fork.c
new file mode 100644
index 0000000..4d7fbd3
--- /dev/null
+++ b/build/has/_Fork.c
@@ -0,0 +1,8 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include <unistd.h>
+
+int main(void) {
+	return _Fork();
+}