[ulib][gpt] Compile with -fvisibility=hidden

ZX-1895 #comment Converted gpt

Change-Id: I90bbcb3f20208e457c4ea7262daf104485d143f8
diff --git a/system/ulib/gpt/rules.mk b/system/ulib/gpt/rules.mk
index 6dcd240..0f58be4 100644
--- a/system/ulib/gpt/rules.mk
+++ b/system/ulib/gpt/rules.mk
@@ -8,6 +8,8 @@
 
 MODULE_TYPE := userlib
 
+MODULE_COMPILEFLAGS += -fvisibility=hidden
+
 MODULE_SRCS += \
     $(LOCAL_DIR)/cros.c \
     $(LOCAL_DIR)/gpt.c \