Move check_functions in meson script

Move the variable to the place it is actually used.

app/meson.build

@@ -76,10 +76,6 @@ if aoa_hid_support
     ]
 endif
 
-check_functions = [
-    'strdup'
-]
-
 cc = meson.get_compiler('c')
 
 if not get_option('crossbuild_windows')
@@ -140,6 +136,10 @@ if host_machine.system() == 'windows'
     dependencies += cc.find_library('ws2_32')
 endif
 
+check_functions = [
+    'strdup',
+]
+
 foreach f : check_functions
   if cc.has_function(f)
     define = 'HAVE_' + f.underscorify().to_upper()