__memcpy_chk: Fix signed cmp of unsigned values.

I accidentally did a signed comparison of the size_t values passed in
for three of the _chk functions. Changing them to unsigned compares.

Add three new tests to verify this failure is fixed.

Bug: 10691831

Merge from internal master.

(cherry-picked from 883ef2499c2ff76605f73b1240f719ca6282e554)

Change-Id: Id9a96b549435f5d9b61dc132cf1082e0e30889f5
diff --git a/libc/arch-arm/krait/bionic/__strcat_chk.S b/libc/arch-arm/krait/bionic/__strcat_chk.S
index ec99077..956b461 100644
--- a/libc/arch-arm/krait/bionic/__strcat_chk.S
+++ b/libc/arch-arm/krait/bionic/__strcat_chk.S
@@ -180,7 +180,7 @@
 .L_strlen_done:
     add     r2, r3, r4
     cmp     r2, lr
-    bgt     __strcat_chk_failed
+    bhi     __strcat_chk_failed
 
     // Set up the registers for the memcpy code.
     mov     r1, r5