Fix for missing /usr/games in root's PATH

After importing the default environment from NetBSD, we discovered that
it doesn't contain /usr/games, which is required for the commands
strfile. This utility is used while generating fortune database.

This patch simply sets TOOL_STRFILE to contain an absolute path.

Change-Id: I2e366a0b67d5258f387c3f5a2a2a581fedead359