Generate assembler system call stubs via genrule.

There's no need to check in generated code.

Test: builds & boots
Change-Id: Ife368bca4349d4adeb0666db590356196b4fbd63
diff --git a/libc/tools/Android.bp b/libc/tools/Android.bp
new file mode 100644
index 0000000..13179a0
--- /dev/null
+++ b/libc/tools/Android.bp
@@ -0,0 +1,4 @@
+filegroup {
+    name: "bionic-gensyscalls",
+    srcs: ["gensyscalls.py"]
+}