Arm32 dynamic function dispatch

Previous change was reverted in 9690b121e342676453c58f5940964350762085a0.
This change added .arch directive to kryo/ to avoid invalid instruction error.

Test: Run bionic unit test.
Test: Use gdb to make sure the right function is selected.
Test: Build previously failed target: make PRODUCT-sdk_phone_arm64-sdk
Change-Id: I14de41851121fc1a0b38c98fda5eb844b6a9695c
diff --git a/libc/arch-arm/krait/bionic/memcpy_base.S b/libc/arch-arm/krait/bionic/memcpy_base.S
index dc8ad2c..5b4b70d 100644
--- a/libc/arch-arm/krait/bionic/memcpy_base.S
+++ b/libc/arch-arm/krait/bionic/memcpy_base.S
@@ -41,8 +41,13 @@
 #endif
 
 	.text
+	.syntax unified
 	.fpu    neon
 
+	// To avoid warning about deprecated instructions, add an explicit
+	// arch. The code generated is exactly the same.
+	.arch armv7-a
+
 .L_memcpy_base:
 	cmp	r2, #4
 	blt	.L_neon_lt4