Fix __must_check compile on older compilers

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/compiler.h b/compiler.h
new file mode 100644
index 0000000..0d17ae1
--- /dev/null
+++ b/compiler.h
@@ -0,0 +1,12 @@
+#ifndef FIO_COMPILER_H
+#define FIO_COMPILER_H
+
+#if __GNUC__ >= 4
+#include "compiler-gcc4.h"
+#elif __GNUC == 3
+#include "compiler-gcc3.h"
+#else
+#error Compiler too old, need gcc at least gcc 3.x
+#endif
+
+#endif