The problem is as described at 
https://gcc.gnu.org/install/specific.html#amdgcn-x-amdhsa

"Note that support for Fiji devices has been removed in ROCm 4.0 and 
support in LLVM is deprecated and will be removed in LLVM 18."

Therefore, GCC is no longer build with Fiji (gfx803) support by default 
– and the -march=fiji testcases now fails as the -lgomp multilib for 
Fiji is not available. (That is: It fails, unless Fiji support has been 
enabled manually.)

Andrew mentioned that there is a PR about this, but I couldn't find it. 
If someone can, I am happy to add it to the changelog.

OK for mainline?

Tobias