Update RACK_USER_DIR in plugin.mk for all OS's.

plugin.mk

@@ -33,20 +33,21 @@ ifdef ARCH_LIN
 	LDFLAGS += -Wl,-rpath=/tmp/Rack2
 	# Since the plugin's compiler could be a different version than Rack's compiler, link libstdc++ and libgcc statically to avoid ABI issues.
 	LDFLAGS += -static-libstdc++ -static-libgcc
-	RACK_USER_DIR ?= $(HOME)/.Rack2
+	XDG_DATA_HOME ?= $(HOME)/.local/share
+	RACK_USER_DIR ?= $(XDG_DATA_HOME)/Rack2
 endif
 
 ifdef ARCH_MAC
 	TARGET := $(TARGET).dylib
 	LDFLAGS += -undefined dynamic_lookup
-	RACK_USER_DIR ?= $(HOME)/Documents/Rack2
+	RACK_USER_DIR ?= $(HOME)/Library/Application Support/Rack2
 	CODESIGN ?= codesign -f -s -
 endif
 
 ifdef ARCH_WIN
 	TARGET := $(TARGET).dll
 	LDFLAGS += -static-libstdc++
-	RACK_USER_DIR ?= $(USERPROFILE)/Documents/Rack2
+	RACK_USER_DIR ?= $(LOCALAPPDATA)/Rack2
 endif
 
 PLUGINS_DIR := $(RACK_USER_DIR)/plugins-$(ARCH_OS)-$(ARCH_CPU)