Fix AC_CHECK_DECL

[Ralf Wildenhues]

AC_CHECK_DECL currently does not work with compilers in picky mode
(-Wall -Werror, for example), and also it does not work at all with
struct objects for example.

The following patch tries to fix that.  I think there could be issues on
systems where pointers to data and pointers to functions are incompatible,
but I don't know a good quick way around that.  Do you think we may need
to, in case the cast to `char *' failed, try another compilation with a
cast to some function pointer?  I think it would probably suffice to
wait for a bug report (the testsuite addition should expose this).

So, OK to apply?

Cheers,
Ralf

        * lib/autoconf/general.m4 (AC_CHECK_DECL): Fix test for struct
        objects by taking the address of the symbol; this also avoids
        warnings for other usage cases with a picky compiler.
        * tests/semantics.at (AC_CHECK_DECLS): Also check macros,
        structure, and function symbols.
        * NEWS: Update.

Index: NEWS
===================================================================
RCS file: /cvsroot/autoconf/autoconf/NEWS,v
retrieving revision 1.401
diff -u -r1.401 NEWS
--- NEWS        26 Sep 2006 06:04:35 -0000      1.401
+++ NEWS        26 Sep 2006 18:10:55 -0000
@@ -13,6 +13,8 @@
   New macro, with the behavior of the 2.60a AC_COMPUTE_INT macro.
   AC_COMPUTE_INT no longer caches or reports results.
 
+** AC_CHECK_DECL now also works with structure objects.
+
 ** GNU M4 1.4.7 or later is now recommended.
 
 * Major changes in Autoconf 2.60a (2006-08-25)
Index: lib/autoconf/general.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/autoconf/general.m4,v
retrieving revision 1.930
diff -u -r1.930 general.m4
--- lib/autoconf/general.m4     14 Sep 2006 09:40:59 -0000      1.930
+++ lib/autoconf/general.m4     26 Sep 2006 18:10:56 -0000
@@ -2546,7 +2546,7 @@
 AC_CACHE_CHECK([whether $1 is declared], ac_Symbol,
 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT([$4])],
 [#ifndef $1
-  char *p = (char *) $1;
+  char *p = (char *) & $1;
   return !p;
 #endif
 ])],
Index: tests/semantics.at
===================================================================
RCS file: /cvsroot/autoconf/autoconf/tests/semantics.at,v
retrieving revision 1.57
diff -u -r1.57 semantics.at
--- tests/semantics.at  26 Sep 2006 18:07:16 -0000      1.57
+++ tests/semantics.at  26 Sep 2006 18:10:56 -0000
@@ -106,10 +106,18 @@
 # Check that it performs the correct actions:
 # Must define NEED_NO_DECL, but not NEED_YES_DECL.
 AT_CHECK_MACRO([AC_CHECK_DECLS],
-[[AC_CHECK_DECLS([yes, no],,,
-                [int yes = 1;])]],
+[[AC_CHECK_DECLS([yes, no, mystruct, myfunc, mymacro1, mymacro2],,,
+                [[int yes = 1;
+                  struct { int x[20]; } mystruct;
+                  extern int myfunc();
+                  #define mymacro1(arg) arg
+                  #define mymacro2]])]],
 [AT_CHECK_DEFINES(
-[#define HAVE_DECL_NO 0
+[#define HAVE_DECL_MYFUNC 1
+#define HAVE_DECL_MYMACRO1 1
+#define HAVE_DECL_MYMACRO2 1
+#define HAVE_DECL_MYSTRUCT 1
+#define HAVE_DECL_NO 0
 #define HAVE_DECL_YES 1
 ])])