bug#25213: Character encoding issue causing broken symlinks for profile generation

[Christopher Baines <mail@cbaines.net>]

The profile generation/union code generates broken symlinks. I've 
reproduced this on 2 different machines (both Debian running Guix).

To reproduce, run:

   guix environment --pure --container --ad-hoc nss-certs findutils 
coreutils

[env]# find $GUIX_ENVIRONMENT/etc/ssl/certs -xtype l -exec head {} \;

head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/Certinomis_-_Autorit??_Racine:2.1.1.pem' 
for reading: No such file or directory
head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/NetLock_Arany_=Class_Gold=_F??tan??s??tv??ny:2.6.73.65.44.228.0.16.pem' 
for reading: No such file or directory
head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/T??RKTRUST_Elektronik_Sertifika_Hizmet_Sa??lay??c??s??_H6:2.6.125.161.242.101.236.138.pem' 
for reading: No such file or directory
head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/AC_Ra??z_Certic??mara_S.A.:2.15.7.126.82.147.123.224.21.227.87.240.105.140.203.236.12.pem' 
for reading: No such file or directory
head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/T??B??TAK_UEKAE_K??k_Sertifika_Hizmet_Sa??lay??c??s??_-_S??r??m_3:2.1.17.pem' 
for reading: No such file or directory
head: cannot open 
'/gnu/store/g41lycan2cq74qfs6acsxmxk4c4ra0pd-profile/etc/ssl/certs/T??RKTRUST_Elektronik_Sertifika_Hizmet_Sa??lay??c??s??_H5:2.7.0.142.23.254.36.32.129.pem' 
for reading: No such file or directory

Note the ?? in the names, which are the points where the names are 
incorrect.

This will cause errors like Throw to key `gnutls-error' with args 
`(#<gnutls-error-enum Error while reading file.> when using Guix.