build: Add new DPKG_CHECK_DECL m4 macro

Used to check if something is declared in a header.

m4/types.m4

@@ -1,3 +1,5 @@
+# Copyright © 2009 Guillem Jover <guillem@debian.org>
+
 # DPKG_TYPE_PTRDIFF_T
 # -------------------
 # Check for the ptrdiff_t type, defining to int if not defined
@@ -21,6 +23,17 @@ AC_CHECK_DECLS([sys_siglist],,,
 ])dnl
 ])# DPKG_DECL_SYS_SIGLIST
 
+# DPKG_CHECK_DECL([DECL], [HEADER])
+# -----------------
+# Define HAVE_DECL to 1 if declared in HEADER
+AC_DEFUN([DPKG_CHECK_DECL],
+[
+  AC_CHECK_DECL($1,
+                [AC_DEFINE([HAVE_]$1, 1,
+                           [Define to 1 if ']$1[' is declared in <$2>])],,
+                [[#include <$2>]])
+])# DPKG_CHECK_DECL
+
 # DPKG_CHECK_DEFINE([DEFINE], [HEADER])
 # -------------------------------------
 # Defines HAVE_DEFINE to 1 if declared in HEADER, 0 otherwise