License changes in Gnatcoll packages

[Björn Persson]

Starting with Fedora 34, several Gnatcoll subpackages have licenses
that include the GCC Runtime Library Exception. The License fields
have therefore changed as follows:

gnatcoll-core, gnatcoll-iconv, gnatcoll-syslog, gnatcoll-sql,
gnatcoll-sqlite and gnatcoll-postgres have changed from GPLv3+ to
GPLv3+ with exceptions.

gnatcoll-gmp, gnatcoll-readline and gnatcoll-xref are still GPLv3+.

Björn Persson