MINOR/BUILD: fix Lua build on Mac OS X

Change gcc option syntax for Mac. -Wl,--export-dynamic is not
supported, use -Wl,-export_dynamic.

Thanks to Kirill A. Korinsky for the report.

This patch should be backported on each version from 1.6

Makefile

@@ -331,6 +331,7 @@ ifeq ($(TARGET),osx)
   USE_POLL       = implicit
   USE_KQUEUE     = implicit
   USE_TPROXY     = implicit
+  EXPORT_SYMBOL  = -export-dynamic
 else
 ifeq ($(TARGET),openbsd)
   # This is for OpenBSD >= 5.7
@@ -630,7 +631,7 @@ check_lua_inc = $(shell if [ -d $(2)$(1) ]; then echo $(2)$(1); fi;)
 
 BUILD_OPTIONS   += $(call ignore_implicit,USE_LUA)
 OPTIONS_CFLAGS  += -DUSE_LUA $(if $(LUA_INC),-I$(LUA_INC))
-LUA_LD_FLAGS := -Wl,--export-dynamic $(if $(LUA_LIB),-L$(LUA_LIB))
+LUA_LD_FLAGS := -Wl,$(if $(EXPORT_SYMBOL),$(EXPORT_SYMBOL),--export-dynamic) $(if $(LUA_LIB),-L$(LUA_LIB))
 ifeq ($(LUA_LIB_NAME),)
 # Try to automatically detect the Lua library
 LUA_LIB_NAME := $(firstword $(foreach lib,lua5.3 lua53 lua,$(call check_lua_lib,$(lib),$(LUA_LD_FLAGS))))