init.rc: add missing /dev/fd symlink

The Linux kernel implicitly expects /dev/fd to symlink to /proc/self/fd.

This change fixes the exec/execveat.c kernel selftest.

Change-Id: Ia08d50023336fdbfc098527299c326d9d59039a9
Signed-off-by: Greg Hackmann <ghackmann@google.com>

rootdir/init.rc

@@ -201,6 +201,10 @@ on init
     # enable armv8_deprecated instruction hooks
     write /proc/sys/abi/swp 1
 
+    # Linux's execveat() syscall may construct paths containing /dev/fd
+    # expecting it to point to /proc/self/fd
+    symlink /proc/self/fd /dev/fd
+
 # Healthd can trigger a full boot from charger mode by signaling this
 # property when the power button is held.
 on property:sys.boot_from_charger_mode=1