Mount /tmp as tmpfs.

/tmp is a volatile temporary storage location for the shell user.
As with /data/local/tmp, it is owned by shell:shell and is chmod 771.

Bug: 311263616
Change-Id: Ice0229d937989b097971d9db434d5589ac2da99a
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 7deb173..7444f96 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -97,7 +97,7 @@
 # create some directories (some are mount points) and symlinks
 LOCAL_POST_INSTALL_CMD := mkdir -p $(addprefix $(TARGET_ROOT_OUT)/, \
     dev proc sys system data data_mirror odm oem acct config storage mnt apex bootstrap-apex debug_ramdisk \
-    linkerconfig second_stage_resources postinstall $(BOARD_ROOT_EXTRA_FOLDERS)); \
+    linkerconfig second_stage_resources postinstall tmp $(BOARD_ROOT_EXTRA_FOLDERS)); \
     ln -sf /system/bin $(TARGET_ROOT_OUT)/bin; \
     ln -sf /system/etc $(TARGET_ROOT_OUT)/etc; \
     ln -sf /data/user_de/0/com.android.shell/files/bugreports $(TARGET_ROOT_OUT)/bugreports; \