Changing CWD of make while it's running

[Lee Shallis]

Here's the relevant snippet of my makefile code:

HERE:=$(dir $(lastword $(MAKEFILE_LIST)))
include $(TOPDIR)target.mk
#include $(TOPDIR)mkfunc/chdir.mk
CURDIR:=$(shell echo $(PWD))$(DIRSEP)
# Directories
PREPARE:=set tmp
REPLACE:=%tmp:teh=the%
#$(call chdir,$(CURDIR)$(TOPDIR))
WKSDIR:=$(shell echo $(PWD))$(DIRSEP)
OBJDIR:=obj
OUTDIR:=build
PRJOUT:=$(OUTDIR)/$(TARDIR)
PRJOBJ:=$(OBJDIR)/$(TARDIR)
B:=$(PRJOUT)/$(DBG)
O:=$(PRJOBJ)/$(DBG)
DEPDIR:=$(OUTDIR) $(PRJOUT) $(OBJDIR) $(PRJOBJ)
PRJINC:=$(FI)"$(CC_INC)" $(FI)"src" $(FI)"$(O)"
PRJBIN:=$(FL)"$(CC_LIB)" $(FL)"$(PRJOUT)"
PRJLIB:=$(FL)"$(CC_LIB)"
SOURCES:=$(wildcard src/*.c)
OBJECTS:=$(patsubst src/%.c,$(O)%.o,$(SOURCES))

The to lines commented out that are obviously actions to be performed are
where I'm having trouble, I initially tried using the $(shell chdir...)
variant but later realized my mistake there, I then went on to googling for
possible solutions to this, I'd rather not start up a new instance of make
just to apply an option to change the working directory, is it possible to
do this from within my makefiles?