meson.build files that use cc.run() in native builds can silently fallback to
meson.get_cross_property() in cross builds without an exe-wrapper, but there's
no way to know that this is happening.

As the defaults may be pessimistic (for example, disabling the support for a
feature that should be enabled) emit a warning when the default is used, so that
the recipe can explicitly set the cross property as relevant.

Upstream-Status: Submitted [https://github.com/mesonbuild/meson/pull/5071]
Signed-off-by: Ross Burton <ross.burton@intel.com>

diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 3c3cfae0..10e741ae 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -1890,6 +1890,7 @@ class MesonMain(InterpreterObject):
             return props[propname]
         except Exception:
             if len(args) == 2:
+                mlog.warning('Cross property %s is using default value %s' % (propname, args[1]))
                 return args[1]
             raise InterpreterException('Unknown cross property: %s.' % propname)