Various C99 compatibility fixes

strrchr is declared in <strings.h>, not <string.h>.

_GNU_SOURCE needs to be defined before any glibc headers are included,
otherwise it is not effective.

Also patch some old autoconf-internal issues in the hydra-gtk
configure script.

configure

@@ -1356,7 +1356,7 @@ echo "Checking for Android specialities ..."
 TMPC=comptest$$
 STRRCHR=" not"
 echo '#include <stdio.h>' > $TMPC.c
-echo '#include <strings.h>' >> $TMPC.c
+echo '#include <string.h>' >> $TMPC.c
 echo "int main() { char *x = strrchr(\"test\", 'e'); if (x == NULL) return 0; else return 1; }" >> $TMPC.c
 $CC -o $TMPC $TMPC.c > /dev/null 2>&1
 test -x $TMPC && STRRCHR=""

hydra-gtk/configure

@@ -2391,7 +2391,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -3192,7 +3192,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -3797,8 +3797,8 @@ main ()
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return 2;
+  return 0;
 }
 _ACEOF
 rm -f conftest$ac_exeext

hydra-rtsp.c

@@ -6,10 +6,11 @@
 //
 //
 
+#define _GNU_SOURCE
+
 #include "hydra-mod.h"
 #include "sasl.h"
 #include <stdio.h>
-#define _GNU_SOURCE
 #include <string.h>
 
 extern char *HYDRA_EXIT;