Installed, just not linked

First run

brew link <package>

If it gives an error, try for an automated diagnosis

brew doctor

brew doctor gives a list of problems that could be leading to errors in installation process.

To fix problems in case of conflicting files, run to get a list of all actions which will be performed by overwrite without actually performing them.

To list all files that would be deleted:

  brew link --overwrite --dry-run <package>

followed by this run which will execute the overwrite, assuming you feel that the actions performed by overwrite will take your system to a more stable state.

To force the link and overwrite all conflicting files:

 brew link --overwrite <package>

Looks like a permission issue. I would try doing this

chmod 755 /usr/local/lib/pkgconfig

This should make that available, then try

brew link valgrind

If that doesn't work I would try doing a check on it

brew doctor