runtime: add _rt0_arm_android_lib

At the moment this function does nothing, runtime initialization is
still done in android.c:init_go_runtime.

Fixes #10358

Change-Id: I1d762383ba61efcbcf0bbc7c77895f5c1dbf8968
Reviewed-on: https://go-review.googlesource.com/8510Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

src/runtime/rt0_android_arm.s

@@ -9,3 +9,9 @@ TEXT _rt0_arm_android(SB),NOSPLIT,$-4
 	MOVW		$4(R13), R1    // argv
 	MOVW		$_rt0_arm_linux1(SB), R4
 	B		(R4)
+
+// This symbol is called when a shared library is loaded.
+TEXT _rt0_arm_android_lib(SB),NOSPLIT,$0
+	// TODO(crawshaw): initialize runtime.
+	// At the moment this is done in mobile/app/android.c:init_go_runtime
+	RET