build: exclude wee8/out from inputs (envoyproxy#13866)

If you build without sandboxing for performance, the output files from
this custom build genrule contained timestamps which caused it to
rebuild every single build.

Signed-off-by: Keith Smiley <keithbsmiley@gmail.com>

bazel/external/wee8.BUILD

@@ -29,7 +29,10 @@ cc_library(
 
 genrule(
     name = "build",
-    srcs = glob(["wee8/**"]),
+    srcs = glob(
+        ["wee8/**"],
+        exclude = ["wee8/out/**"],
+    ),
     outs = [
         "libwee8.a",
     ],