Switch to the more common idiom for scripts in genrules.

Bug: http://b/198619163
Test: treehugger
Change-Id: I8a6e9e179aef45e1b0622a2e15f80f92041f9736
diff --git a/libc/tools/Android.bp b/libc/tools/Android.bp
index 116b853..c7fce64 100644
--- a/libc/tools/Android.bp
+++ b/libc/tools/Android.bp
@@ -8,8 +8,8 @@
     default_applicable_licenses: ["bionic_libc_license"],
 }
 
-filegroup {
-    name: "bionic-gensyscalls",
+python_binary_host {
+    name: "gensyscalls",
     srcs: ["gensyscalls.py"],
 }