configure.ac: Add missing AM_PROG_CC_C_O.

This causes a warning/error during ./autogen.sh otherwise, at least
on OpenBSD.

Makefile.am:26: warning: compiling 'main.c' with per-target flags requires
'AM_PROG_CC_C_O' in 'configure.ac'.

diff --git a/configure.ac b/configure.ac
index eaa1d9dc29550ae4377945642cbe20f874de215a..dc99626d80e8e08e7f540da81ca043f24bdb66f2 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -42,6 +42,9 @@ CFLAGS="$CFLAGS -Wall -Wextra"
 AC_PROG_CC
 AC_PROG_INSTALL
 
+# Needed for per-target flags or subdir-objects with C sources.
+AM_PROG_CC_C_O
+
 # Initialize libtool.
 LT_INIT