--- mkmf.rb	2011-08-23 13:34:33.853087200 +0200
+++ /Ruby19/lib/ruby/1.9.1/mkmf.rb	2011-10-18 09:57:52.566000000 +0200
@@ -620,13 +620,15 @@
 #{headers}
 /*top*/
 #{MAIN_DOES_NOTHING}
-int t() { #{decltype["volatile p"]}; p = (#{decltype[]})#{func}; return 0; }
+extern int t(void);
+int t(void) { #{decltype["volatile p"]}; p = (#{decltype[]})#{func}; return 0; }
 SRC
   call && try_link(<<"SRC", libs, &b)
 #{headers}
 /*top*/
 #{MAIN_DOES_NOTHING}
-int t() { #{func}(); return 0; }
+extern int t(void);
+int t(void) { #{func}(); return 0; }
 SRC
 end
 
@@ -637,7 +639,8 @@
 #{headers}
 /*top*/
 #{MAIN_DOES_NOTHING}
-int t() { const volatile void *volatile p; p = &(&#{var})[0]; return 0; }
+extern int t(void);
+int t(void) { const volatile void *volatile p; p = &(&#{var})[0]; return 0; }
 SRC
 end
 
@@ -1244,7 +1247,8 @@
 /*top*/
 volatile #{type} conftestval;
 #{MAIN_DOES_NOTHING}
-int t() {return (int)(1-*(conftestval#{member ? ".#{member}" : ""}));}
+extern int t(void);
+int t(void) {return (int)(1-*(conftestval#{member ? ".#{member}" : ""}));}
 SRC
 end
 
@@ -1256,7 +1260,8 @@
 /*top*/
 volatile #{type} conftestval;
 #{MAIN_DOES_NOTHING}
-int t() {return (int)(1-(conftestval#{member ? ".#{member}" : ""}));}
+extern int t(void);
+int t(void) {return (int)(1-(conftestval#{member ? ".#{member}" : ""}));}
 SRC
 end
 
@@ -2274,7 +2279,7 @@
 LIBPATHFLAG = config_string('LIBPATHFLAG') || ' -L"%s"'
 RPATHFLAG = config_string('RPATHFLAG') || ''
 LIBARG = config_string('LIBARG') || '-l%s'
-MAIN_DOES_NOTHING = config_string('MAIN_DOES_NOTHING') || 'int main() {return 0;}'
+MAIN_DOES_NOTHING = config_string('MAIN_DOES_NOTHING') || 'int main(void) {return 0;}'
 UNIVERSAL_INTS = config_string('UNIVERSAL_INTS') {|s| Shellwords.shellwords(s)} ||
   %w[int short long long\ long]