When installing rust-debugsource, files such as c_str.rs do not make it into
the package. gdb is therefore unable to display source. c_str.rs however can be
found in the rust-src package, which is a possible alternative, if you consider
adding a suitable Requires: to the debugsource package.

Furthermore, the path that is embedded in programs (e.g. librsvg here) is
wrong:

18:36 axp:~ # gdb /usr/bin/xfce4-settings-manager
/tmp/core.\!usr\!bin\!xfce4-settings-manager.10269 
Core was generated by `/usr/bin/xfce4-settings-manager'.
Program terminated with signal SIGILL, Illegal instruction.
#0  0xb3e18a53 in <&str as
std::ffi::c_str::CString::new::SpecIntoVec>::into_vec () from
/usr/lib/librsvg-2.so.2
[Current thread is 1 (Thread 0xb5fed940 (LWP 10269))]
Missing separate debuginfos, [...]
(gdb) up
#1  0xb3d44649 in std::ffi::c_str::CString::new (t=...)
    at /home/abuild/rpmbuild/BUILD/rustc-1.40.0-src/src/libstd/ffi/c_str.rs:354
354             Self::_new(SpecIntoVec::into_vec(t))


By making a symlink at the location
/home/abuild/rpmbuild/BUILD/rustc-1.40.0-src and pointing to
/usr/lib/rustlib/src/rust, I could work around the issue temporarily.