gdb/testsuite: update bug numbers from Gnats to bugzilla

Some tests link to outdated bug numbers when an XFAIL or a KFAIL happen.

gdb.base/macscp.exp was referencing bug number 555, and the bug 7660
mentions that it used to be 555 on the Gnats system and seems to relate
to the issue at hand.

gdb.base/annota1.exp was referencing bug number 1270, and bug 8375
mentions being number 1270 on Gnats, and mentions annota1 specifically,
so it seemed pretty obvious.
2 files changed