This patch fixes PR111966, i.e. when compiling offloaded code with "-g" 
but without "-march=", mkoffload created a file with e_flags set to 
gfx803/fiji as architecture - while all other files used gfx900, which 
the linker did not like.

Reason: When the default was changed, this flag was missed. When passing 
-march=... instead of relying on the default, it works.

Additionally, it fixed a bug with dangling pointers and multiple 
deletion attempts for the same file, leading normally only to the 
accumulation of /tmp/cc*.mkoffload.dbg.o files.

And, finally,  when building with a recent GCC; it warned about missing 
%<...%> or %qs quotes. I added a couple to reduce the number of warnings.

OK for mainline? — I think the /tmp/cc*.mkoffload.dbg.o part of the 
patch could also be backported to GCC 13 (and 12) if deemed to be useful.

Tobias