Setting PATH from withing make for $(shell) ?

[Cesar Crusius]

Hi there,

Here's my problem: I'm trying to set up a build system where all the 
executables necessary to build something are in the repository itself. So I 
want the build to fail if it requires any executable not in the repository.
The obvious thing to do was

PATH := $(PATH_TO_REPOSITORY_EXECS)

but that doesn't work as it doesn't set the environment variable. For example, 
if after that I do

$(warning $(shell which gcc))

I still get /usr/bin/gcc.

Exporting the variable also doesn't work unless I call make again. But I can't 
do that because I want to preserve the target specified in the command line 
originally.

Using make 3.80 here.

Any help would be greatly appreciated. Best,

- Cesar