GNU Make: "pipe: No such file or directory" error

I'm trying to create a Makefile that works on both Windows and Linux. Running make clean generates the following error:

process_begin: CreateProcess(NULL, rmdir /s /q D:\Documents\Programming\project\bin, ...) failed.
make: Makefile:13: pipe: No such file or directory
process_begin: CreateProcess(NULL, rmdir /s /q D:\Documents\Programming\project\obj, ...) failed.
make: Makefile:15: pipe: No such file or directory

The relevant parts of the Makefile are:

BIN_DIR=bin
OBJ_DIR=obj
SRC_DIR=src

ifeq ($(OS),Windows_NT)
    RMDIR=$(shell rmdir /s /q $(subst /,\,$(abspath $1)))
else
    RMDIR=$(shell rm -rf $(abspath $1))
endif

clean:
    @echo "RM $(BIN_DIR)"
    @$(call RMDIR,$(BIN_DIR))
    @echo "RM $(OBJ_DIR)"
    @$(call RMDIR,$(OBJ_DIR))
    @echo "Done!"

.PHONY: clean

The project structure looks like this:

├─bin
├─obj
├─src
└─Makefile