A couple of things enclose code in "[code] [\code]" to make it easier to read ( without the quotes ).
add a space before each of the "\" like so
Code:
INSTDIR=/tmp/LFS
install: myapp
@if [ -d $(INSTDIR) ]; \
then \
cp myapp $(INSTDIR) && \
chmod a+x $(INSTDIR)/myapp && \
chmod og-w $(INSTDIR)/myapp && \
echo "Installed in $(INSTDIR)"; \
else \
echo "Sorry,$(INSTDIR) does not exist" ;false ; \
fi