[ulib][pretty] Add -fvisibility=hidden

ZX-1895 #comment Converted pretty

Change-Id: Ib76adc340206652e6fcf10683b8c4c6846be0eec
diff --git a/system/ulib/pretty/rules.mk b/system/ulib/pretty/rules.mk
index 59cd6a6..ad48703 100644
--- a/system/ulib/pretty/rules.mk
+++ b/system/ulib/pretty/rules.mk
@@ -8,6 +8,8 @@
 
 MODULE_TYPE := userlib
 
+MODULE_COMPILEFLAGS += -fvisibility=hidden
+
 MODULE_SRCS += \
     $(LOCAL_DIR)/hexdump.c \
     $(LOCAL_DIR)/sizes.c