Enabled AM_PROG_CC_C_O. According to the automake manual, specifying this flag is required when using per-target flags.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@7736 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/configure.in b/configure.in
index 811148b..6ed26fa 100644
--- a/configure.in
+++ b/configure.in
@@ -55,7 +55,7 @@
 
 AC_PROG_LN_S
 AC_PROG_CC
-##AM_PROG_CC_C_O
+AM_PROG_CC_C_O
 AC_PROG_CPP
 AC_PROG_CXX
 AC_PROG_RANLIB