Makefile: don't touch LDFLAGS

These are more like LIBS rather than LDFLAGS.
They are used just in one place,
so simply put them inline.

Also, use LDFLAGS provided by the user during actual link.

This helps users pass their own LDFLAGS.
For example, this is important on Gentoo,
where LDFLAGS='-Wl,-O1 -Wl,--as-needed' is passed by default.

Makefile

@@ -58,7 +58,6 @@ CFLAGS      = -g -Wall \
               -DFUSE_USE_VERSION=29 \
               -MMD \
 	      -DUGID_USE_RWLOCK=$(UGID_USE_RWLOCK)
-LDFLAGS       = -pthread -lrt
 
 PREFIX        = /usr/local
 EXEC_PREFIX   = $(PREFIX)
@@ -86,7 +85,7 @@ help:
 
 $(TARGET): version obj/obj-stamp libfuse/lib/.libs/libfuse.a $(OBJ)
 	cd libfuse && make
-	$(CXX) $(CFLAGS) $(OBJ) -o $@ libfuse/lib/.libs/libfuse.a -ldl $(LDFLAGS)
+	$(CXX) $(CFLAGS) $(LDFLAGS) $(OBJ) -o $@ libfuse/lib/.libs/libfuse.a -ldl -pthread -lrt
 
 mount.mergerfs: $(TARGET)
 	$(LN) -fs "$<" "$@"
@@ -208,7 +207,7 @@ else ifeq ($(shell test -e /usr/bin/yum; echo $$?),0)
 	yum -y install git rpm-build libattr-devel gcc-c++ make which python automake libtool gettext-devel
 endif
 
-unexport CFLAGS LDFLAGS
+unexport CFLAGS
 .PHONY: libfuse_Makefile
 libfuse_Makefile:
 ifeq ($(shell test -e libfuse/Makefile; echo $$?),1)