Instead of hard coding the debug directory to that of the user profile, use
Guile scripting in combination with a new search path specification on GDB to
specify the debug file directories.
* gnu/packages/gdb.scm (gdb-9.1): Add a search path specification for the
GDB_DEBUG_FILE_DIRECTORY environment variable.
* gnu/system/shadow.scm (default-skeletons)[gdbinit]: Derive the value of
DEBUG-FILE-DIRECTORY via the GDB_DEBUG_FILE_DIRECTORY environment variable.
* doc/guix.texi (Installing Debugging Files): Document it.