Only set CWARNFLAGS to gnu flags if $GCC is set. Otherwise check for Sun compiler and use its enhanced warning flag.

configure.ac

@@ -106,8 +106,15 @@ AC_HELP_STRING([--without-debug],    [compile without debugging]),
 AC_CACHE_CHECK([what debugging options to apply], [CDEBUGFLAGS], [CDEBUGFLAGS="-g"])
 AC_SUBST(CDEBUGFLAGS)
 
+if  test "x$GCC" = xyes ; then
     CWARNFLAGS="-Wall -pedantic -Wpointer-arith \
 		-Wstrict-prototypes -Wmissing-declarations -Wnested-externs"
+else
+    AC_CHECK_DECL([__SUNPRO_C], [SUNCC="yes"], [SUNCC="no"])
+    if test "x$SUNCC" = "xyes"; then
+	CWARNFLAGS="-v"
+    fi
+fi
 AC_SUBST(CWARNFLAGS)
 
 GCC_CHECK_VISIBILITY()