fix for overly-picky AC_HEADER_STDBOOL

[Paul Eggert]

I installed this:

2006-05-14  Paul Eggert  <address@hidden>

        * lib/autoconf/headers.m4 (AC_HEADER_STDBOOL): Fix overly-picky
        test for C99 conformance; (bool) 0.5 is an integer constant
        expression, but (bool) -0.5 is not.  Problem reported by Fedor
        Sergeev in <http://forum.sun.com/jive/thread.jspa?threadID=96202>.

--- lib/autoconf/headers.m4     24 Apr 2006 06:51:53 -0000      1.49
+++ lib/autoconf/headers.m4     15 May 2006 02:22:28 -0000      1.50
@@ -582,9 +582,9 @@ AC_DEFUN([AC_HEADER_STDBOOL],
        char a[true == 1 ? 1 : -1];
        char b[false == 0 ? 1 : -1];
        char c[__bool_true_false_are_defined == 1 ? 1 : -1];
-       char d[(bool) -0.5 == true ? 1 : -1];
+       char d[(bool) 0.5 == true ? 1 : -1];
        bool e = &s;
-       char f[(_Bool) -0.0 == false ? 1 : -1];
+       char f[(_Bool) 0.0 == false ? 1 : -1];
        char g[true];
        char h[sizeof (_Bool)];
        char i[sizeof s.t];