build-sys: meson: Fix some defines for default.pa generation

Removes a warning from HAVE_GCONF not being set, and fixes generation of
a large section that depends on OS_IS_WIN32 being explicitly set to 0.

We can't set OS_IS_WIN32 to 0 by default since a bunch of code uses it
via an ifdef rather than by value.
diff --git a/src/daemon/meson.build b/src/daemon/meson.build
index 571c5e2..7f075b0 100644
--- a/src/daemon/meson.build
+++ b/src/daemon/meson.build
@@ -93,6 +93,9 @@
 default_conf.set('PA_BINARY', cdata.get_unquoted('PA_BINARY'))
 default_conf.set('PA_SOEXT', cdata.get_unquoted('PA_SOEXT'))
 default_conf.set10('HAVE_AF_UNIX', cc.has_header('sys/un.h'))
+default_conf.set10('OS_IS_WIN32', host_machine.system() == 'windows')
+# We don't support the deprecated GConf option in meson
+default_conf.set10('HAVE_GCONF', 0)
 
 default_template_file = configure_file(
   input : 'default.pa.in',