build: Fix config.h macros

We have to emulate AC_CHECK_DECLS. Instead of leaving the macro
undefined if a symbol wasn't found, it has to be set to 0.

config.h.cmake.in

@@ -1,6 +1,14 @@
 /* Define to 1 if you have the <arpa/inet.h> header file. */
 #cmakedefine HAVE_ARPA_INET_H 1
 
+/* Define to 1 if you have the declaration of 'getentropy', and to 0 if you
+   don't. */
+#cmakedefine01 HAVE_DECL_GETENTROPY
+
+/* Define to 1 if you have the declaration of 'mmap', and to 0 if you don't.
+   */
+#cmakedefine01 HAVE_DECL_MMAP
+
 /* Define if __attribute__((destructor)) is accepted */
 #cmakedefine HAVE_FUNC_ATTRIBUTE_DESTRUCTOR 1
 
@@ -13,18 +21,12 @@
 /* Define to 1 if you have the <dl.h> header file. */
 #cmakedefine HAVE_DL_H 1
 
-/* Define to 1 if you have the `getentropy' function. */
-#cmakedefine HAVE_DECL_GETENTROPY 1
-
 /* Define if history library is there (-lhistory) */
 #cmakedefine HAVE_LIBHISTORY 1
 
 /* Define if readline library is there (-lreadline) */
 #cmakedefine HAVE_LIBREADLINE 1
 
-/* Define to 1 if you have the `mmap' function. */
-#cmakedefine HAVE_DECL_MMAP 1
-
 /* Define to 1 if you have the <netdb.h> header file. */
 #cmakedefine HAVE_NETDB_H 1
 

meson.build

@@ -261,9 +261,7 @@ xml_check_functions = [
 ]
 
 foreach function : xml_check_functions
-    if cc.has_header_symbol(function[1], function[0])
-        config_h.set10(function[2], true)
-    endif
+    config_h.set10(function[2], cc.has_header_symbol(function[1], function[0]))
 endforeach
 
 # library