Make the fakebins executable to please new symlink target check.

https://r.android.com/1439191 added a check that the prebuilt is
executable for binaries. That failed on the ART APEX check fakebins,
although it didn't abort the builds.

Test: m art-check-{release,debug,testing}-apex-gen-fakebin
Change-Id: I7ed2421e5c800f7dfe09d7ec9c9cfe5123f046e6
diff --git a/build/apex/Android.bp b/build/apex/Android.bp
index 298dece..03b773d 100644
--- a/build/apex/Android.bp
+++ b/build/apex/Android.bp
@@ -414,7 +414,8 @@
     cmd: art_check_apex_gen_stem +
         " --flavor release" +
         " $(in)" +
-        " && touch $(out)",
+        " && touch $(out)" +
+        " && chmod a+x $(out)",
     out: ["art-check-release-apex-gen.unused"],
 }
 
@@ -431,7 +432,8 @@
     cmd: art_check_apex_gen_stem +
         " --flavor debug" +
         " $(in)" +
-        " && touch $(out)",
+        " && touch $(out)" +
+        " && chmod a+x $(out)",
     out: ["art-check-debug-apex-gen.unused"],
 }
 
@@ -448,7 +450,8 @@
     cmd: art_check_apex_gen_stem +
         " --flavor testing" +
         " $(in)" +
-        " && touch $(out)",
+        " && touch $(out)" +
+        " && chmod a+x $(out)",
     out: ["art-check-testing-apex-gen.unused"],
 }