configure.ac: Add missing AM_PROG_CC_C_O.

diff --git a/configure.ac b/configure.ac
index 7621f6e586559e8b3a0a6519b4a5ecebc387807c..908afe9a905022d90ec413a10beee59eac36b884 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -52,6 +52,9 @@ AC_PROG_CPP
 AC_PROG_INSTALL
 AC_PROG_LN_S
 
+# Required for per-target flags or subdir-objects with C sources.
+AM_PROG_CC_C_O
+
 # Initialize libtool.
 LT_INIT