move to C99, fix C++

Index: m4/devil-definitions.m4
--- m4/devil-definitions.m4.orig
+++ m4/devil-definitions.m4
@@ -6,6 +6,8 @@ dnl          ILU_CFLAGS="$ILU_CFLAGS $1"
 dnl          ILUT_CFLAGS="$ILUT_CFLAGS $1"])
 dnl IL_CFLAGS are present everywhere
 
+AC_DEFUN([ADD_ONLY_CFLAGS],
+	 [ONLY_CFLAGS="$ONLY_CFLAGS $1"])
 
 dnl
 dnl Check CPU Extensions
@@ -244,12 +246,12 @@ AC_DEFUN([SETTLE_MNG],
 
 AC_DEFUN([SETTLE_PNG],
          [DEVIL_IL_LIB([png.h],
-                       [png12]) 
-          AS_IF([test "x$have_png12" = "xno"],
+                       [png]) 
+          AS_IF([test "x$have_png" = "xno"],
                 [DEVIL_IL_LIB([png.h],
                               [png]) 
                  lib_test_result="$have_png"],
-                [lib_test_result="$have_png12"]) 
+                [lib_test_result="$have_png"]) 
           AS_IF([test "x$lib_test_result" = "xyes"],
                 [MAYBE_OPTIONAL_DEPENDENCY([IL],
                                            [libpng]) ]) ]) 
@@ -285,14 +287,14 @@ AC_DEFUN([DEVIL_CHECK_RESTRICT],
 
 AC_DEFUN([DEVIL_CHECK_RESTRICT_GNU99],
          [TMP_CFLAGS="$CFLAGS"
-          CFLAGS="$CFLAGS -std=gnu99 -fgnu89-inline"
-          AC_MSG_CHECKING([restrict gnu99 keyword])
+          CFLAGS="$CFLAGS -std=c99 -fgnu89-inline"
+          AC_MSG_CHECKING([restrict c99 keyword])
           AC_COMPILE_IFELSE([[void foo(void * restrict test){}]],
 	                    [AC_DEFINE([RESTRICT_KEYWORD],
 	  			       [1],
 				       [restric keyword available])
 	                     AC_MSG_RESULT([yes])
 	                     CFLAGS="$TMP_CFLAGS"
-                             ADD_CFLAGS(-std=gnu99 -fgnu89-inline)],
+                             ADD_ONLY_CFLAGS(-std=c99 -fgnu89-inline)],
 			    [AC_MSG_RESULT([no])
 	                     CFLAGS="$TMP_CFLAGS"]) ])