configure.ac : Add AM_PROG_CC_C_O.
diff --git a/configure.ac b/configure.ac
index 37e5610..d2501bb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -57,6 +57,7 @@
 
 # c flavor
 AC_HEADER_STDC
+AM_PROG_CC_C_O
 AC_C_INLINE
 AC_C_VARARRAYS