Port the GNU/Linux parts of config.guess to C99 because the script is
invoked without CFLAGS.

diff --git a/autoconf/config.guess b/autoconf/config.guess
index 41249c1295106577..bf567065edc492a6 100755
--- a/autoconf/config.guess
+++ b/autoconf/config.guess
@@ -686,7 +686,8 @@ EOF
 	  # Determine whether the default compiler is a.out or elf
 	  cat >dummy.c <<EOF
 #include <features.h>
-main(argc, argv)
+#include <stdio.h>
+int main(argc, argv)
      int argc;
      char *argv[];
 {
@@ -900,7 +901,7 @@ cat >dummy.c <<EOF
 # include <sys/types.h>
 # include <sys/utsname.h>
 #endif
-main ()
+int main (void)
 {
 #if defined (sony)
 #if defined (MIPSEB)