In 9253e1206e a bunch of `gdbr-check` (for `rust-gdb`) and
`gdbg-check` (for plain `gdb`) was added. But in two places the author
accidentally wrote `gdbt-check` instead. This commit fixes this typo.
Disabling loading of pretty printers in the debugger itself is more
reliable. Before this commit the .gdb_debug_scripts section couldn't be
included in dylibs or rlibs as otherwise there is no way to disable the
section anymore without recompiling the entire standard library.
