Check for cc before gcc.

If cc is something other than gcc and is the system compiler prefer using
that, unless otherwise told via $CC.  ok djm@

configure.ac

@@ -19,7 +19,7 @@ AC_CONFIG_SRCDIR([ssh.c])
 AC_LANG([C])
 
 AC_CONFIG_HEADER([config.h])
-AC_PROG_CC
+AC_PROG_CC([cc gcc])
 AC_CANONICAL_HOST
 AC_C_BIGENDIAN