Clearing the standard search path

[Harvey Chapman <hchapman-gcc-help at 3gfp dot com>]

I've looked through the manuals for gcc and ld, but would like some 
advice regarding ignoring standard search paths for headers and 
libraries. I've found "-nostdinc" for gcc and "-z nodefaultlib 
-nostdlib" for ld.

I'm trying to build an embedded OS in a separate directory and I want to 
ensure that missing dependencies (in my destination directory) are not 
automatically found in Ubuntu's standard paths (/usr/include, /usr/lib, 
etc.). I figured that if I could clear the standard search paths, the 
compiles would fail alerting me instantly about a missing dependency.

I need to find the most portable way to do this that will work with as 
many "./configure; make; make install" style packages. Should I use the 
flags above inside CFLAGS and LDFLAGS variables? Or should I set CPATH 
equal to nothing?

Thanks for the help,

Harvey