Add stpcpy assembler version.

For generic, continue to use the C version of the code.

Bug: 13746695

(cherry picked from commit 7d849ac378515efa1522e538e6e1d3b546cae97d)

Change-Id: Iae44785f37f9bb59103ab78fb9f74c92f8a95c7f
diff --git a/libc/arch-arm/generic/generic.mk b/libc/arch-arm/generic/generic.mk
index 2456e6e..95be867 100644
--- a/libc/arch-arm/generic/generic.mk
+++ b/libc/arch-arm/generic/generic.mk
@@ -7,4 +7,5 @@
     bionic/memmove.c \
     bionic/__strcat_chk.cpp \
     bionic/__strcpy_chk.cpp \
+    upstream-openbsd/lib/libc/string/stpcpy.c \
     upstream-openbsd/lib/libc/string/strcat.c \