Switch to current OpenBSD system.c.

Change-Id: Ie2df60f0d55dca69149ffe064f10183411407987
diff --git a/libc/Android.mk b/libc/Android.mk
index 9ab7e8e..e401a1c 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -106,7 +106,6 @@
     stdlib/strtod.c \
     unistd/alarm.c \
     unistd/syslog.c \
-    unistd/system.c \
     unistd/time.c \
 
 # Fortify implementations of libc functions.
@@ -388,6 +387,7 @@
     upstream-openbsd/lib/libc/stdlib/strtoumax.c \
     upstream-openbsd/lib/libc/stdlib/strtoll.c \
     upstream-openbsd/lib/libc/stdlib/strtol.c \
+    upstream-openbsd/lib/libc/stdlib/system.c \
     upstream-openbsd/lib/libc/locale/wcsxfrm.c \
 
 libc_arch_static_src_files := \