Enforce go/cras-style#build-time-feature-switches in define_feature

BUG=None
TEST=try to define a feature switch named FOO_BAR and Bazel complains about it

Change-Id: I36100c59a9bc7699c7316e2de5a13c323c0f9e14
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/6126535
Commit-Queue: Li-Yu Yu <[email protected]>
Tested-by: [email protected] <[email protected]>
Reviewed-by: Terry Cheong <[email protected]>

Author: afq984

utils.bzl

@@ -21,6 +21,8 @@ def bool_flag_config(name, build_setting_default):
 
 def define_feature(condition, define):
     """Defines `define`=1 if condition is true, otherwise 0"""
+    if not define.startswith(("CRAS_", "HAVE_")):
+        fail("Invalid feature switch %r. Feature switch names must start with CRAS_ or HAVE_. See go/cras-style#build-time-feature-switches" % define)
     return select({
         condition: ["{}=1".format(define)],
         "//conditions:default": ["{}=0".format(define)],