Fix incorrect checking of build machine for dependency availability

Don't check the build machine to determine a dependency whose availability
is static property of the host machine

mesonbuild/dependencies/platform.py

@@ -33,7 +33,7 @@ class AppleFrameworks(ExternalDependency):
         for f in self.frameworks:
             self.link_args += ['-framework', f]
 
-        self.is_found = mesonlib.is_osx()
+        self.is_found = mesonlib.for_darwin(self.want_cross, self.env)
 
     def log_tried(self):
         return 'framework'

mesonbuild/dependencies/ui.py

@@ -39,13 +39,13 @@ class GLDependency(ExternalDependency):
     def __init__(self, environment, kwargs):
         super().__init__('gl', environment, None, kwargs)
 
-        if mesonlib.is_osx():
+        if mesonlib.for_darwin(self.want_cross, self.env):
             self.is_found = True
             # FIXME: Use AppleFrameworks dependency
             self.link_args = ['-framework', 'OpenGL']
             # FIXME: Detect version using self.clib_compiler
             return
-        if mesonlib.is_windows():
+        if mesonlib.for_windows(self.want_cross, self.env):
             self.is_found = True
             # FIXME: Use self.clib_compiler.find_library()
             self.link_args = ['-lopengl32']