bug#25848: [PATCH] gnu: %bootstrap-coreutils&co: Patch egrep/fgrep to point to the correct grep.

[manolis837]

Hello everyone, 

Commit 653add37af10b0d5dbc20c8bc7ce30eec8cf4ae7 patches egrep/fgrep to point to 
the location of grep. 
But the problem is that when it was run on Hurd, the path for grep in 
egrep/fgrep had this form: 
/gnu/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-grep-2.25/bin/grep

The above was not being substituted and caused the build to fail. So I changed 
the pattern to 
"/[^ ]+/bin/grep" and now the path is always replaced. 

Also (getcwd) returns the current path which the build takes place. This 
happens to be /tmp/guix-build-..-bootstrap-binaries-0.
This is wrong because it should point to the final place in /gnu/store. That 
why I am using "out".

Thank you,
Manolis