Checks whether right shift extends the sign bit.

Patch by Thomas Wouters <thomas@xs4all.net> with small changes of mine
(in main(), use return instead of exit).

Closes patch #100832
(but I can't assign it to myself, nor close it -- sorry)

configure.in

@@ -1136,6 +1136,19 @@ AC_MSG_RESULT($usable_wchar_t)
 # check for endianness
 AC_C_BIGENDIAN
 
+# Check whether right shifting a negative integer extends the sign bit
+# or fills with zeros (like the Cray J90, according to Tim Peters).
+AC_MSG_CHECKING(whether right shift extends the sign bit)
+AC_TRY_RUN([
+int main()
+{
+	return ((-1)>>3 == -1) ? 1 : 0;
+}
+],
+[AC_DEFINE(SIGNED_RIGHT_SHIFT_ZERO_FILLS)
+ AC_MSG_RESULT(yes)],
+[AC_MSG_RESULT(no)])
+
 # THIS MUST BE LAST, IT CAN BREAK OTHER TESTS!
 # Add sys/socket.h to confdefs.h
 cat >> confdefs.h <<\EOF