bug#19973: Grafts break debug outputs

[Mark H Weaver]

Grafts break debug outputs, or at least that's my guess.
Here's what I see:

address@hidden:~$ guix build guile
guix build: warning: ambiguous package specification `guile'
guix build: warning: choosing guile-2.0.11 from gnu/packages/guile.scm:110:2
/gnu/store/3lhr8q28q6f59774di9av7ncy09jd55d-guile-2.0.11
/gnu/store/rgv3fvy6xqp6966rfh8v6fv7m48abcbh-guile-2.0.11-debug
address@hidden:~$ guix package -I guile
guile   2.0.11  out     /gnu/store/3lhr8q28q6f59774di9av7ncy09jd55d-guile-2.0.11
guile   2.0.11  debug   
/gnu/store/rgv3fvy6xqp6966rfh8v6fv7m48abcbh-guile-2.0.11-debug
address@hidden:~$ ls -l .guix-profile/lib/debug/gnu/store/
total 8
lrwxrwxrwx 12 root guixbuild 128 Dec 31  1969 
122jv790mv2mlnylbrbzav65vghbw93n-guile-2.0.11 -> 
/gnu/store/rgv3fvy6xqp6966rfh8v6fv7m48abcbh-guile-2.0.11-debug/lib/debug/gnu/store/122jv790mv2mlnylbrbzav65vghbw93n-guile-2.0.11
lrwxrwxrwx 15 root guixbuild 127 Dec 31  1969 
3g20rdmnavpblsmgppyl8jhg67nidhjk-glibc-2.20 -> 
/gnu/store/hrny2whqg9c3m0klyfpbmmcyiir9yf8m-gcc-toolchain-4.9.2/lib/debug/gnu/store/3g20rdmnavpblsmgppyl8jhg67nidhjk-glibc-2.20

I guess GDB can't find the debugging information because
122jv790mv2mlnylbrbzav65vghbw93n-guile-2.0.11 is the name of the guile
directory *before* grafting.

To work around this, I created my own ~/mydebug directory:

address@hidden:~/mydebug/gnu/store$ ln -s 
/gnu/store/rgv3fvy6xqp6966rfh8v6fv7m48abcbh-guile-2.0.11-debug/lib/debug/gnu/store/122jv790mv2mlnylbrbzav65vghbw93n-guile-2.0.11
 3lhr8q28q6f59774di9av7ncy09jd55d-guile-2.0.11

and then pointed GDB at ~/mydebug and then debugging works again.

      Mark