Add long double check support to configure test.

configure.in

@@ -1321,6 +1321,17 @@ if test "$have_long_long" = yes ; then
 AC_CHECK_SIZEOF(long long, 8)
 fi
 
+AC_MSG_CHECKING(for long double support)
+have_long_double=no
+AC_TRY_COMPILE([], [long double x; x = (long double)0.;], [
+  AC_DEFINE(HAVE_LONG_DOUBLE, 1, [Define this if you have the type long double.])
+  have_long_double=yes
+])
+AC_MSG_RESULT($have_long_double)
+if test "$have_long_long" = yes ; then
+AC_CHECK_SIZEOF(long double, 12)
+fi
+
 AC_MSG_CHECKING(for _Bool support)
 have_c99_bool=no
 AC_TRY_COMPILE([], [_Bool x; x = (_Bool)0;], [