Add posix_* weak helpers

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/helpers.c b/helpers.c
new file mode 100644
index 0000000..987f5b6
--- /dev/null
+++ b/helpers.c
@@ -0,0 +1,15 @@
+#include <malloc.h>
+#include <stdlib.h>
+
+#include "compiler/compiler.h"
+
+int __weak posix_memalign(void **ptr, size_t align, size_t size)
+{
+	*ptr = memalign(align, size);
+	return *ptr == NULL;
+}
+
+int __weak posix_fallocate(int fd, off_t offset, off_t len)
+{
+	return 0;
+}