[Libomptarget][AMDGCN] add gfx90c target

[ye-luo]

ROCm 5.0.0 requires me to use this target on my 4700u

[JonChesterfield]

That's somewhat interesting, @arsenm the 4000 series APUs used to identify as gfx902 iirc - does the new name for existing hardware make sense to you?

90c introduced in https://reviews.llvm.org/D90419, only change I can see in that a change to sramecc, which I thought was a targetid thing and not an isa thing. It does name various APUs as now corresponding to 90c though. So this change is fine.

[ye-luo]

I was using gfx902 in the past but after installing ROCm 5.0.0 today, I got a complaint and I have to use gfx90c by copying gfx902 bc files to gfx90c.
However it is better to do the right thing here.

openmp/libomptarget/DeviceRTL/CMakeLists.txt

 
 # Check all SM values
 foreach(sm ${nvptx_sm_list})
   if (NOT ${sm} IN_LIST all_capabilities)
     libomptarget_warning_say("[NVPTX] Compute capability ${sm} is not supported. Make sure clang can work with it.")
   endif()
 endforeach()
 
-set(amdgpu_mcpus gfx700 gfx701 gfx801 gfx803 gfx900 gfx902 gfx906 gfx908 gfx90a gfx1010 gfx1030 gfx1031)
+set(amdgpu_mcpus gfx700 gfx701 gfx801 gfx803 gfx900 gfx902 gfx906 gfx908 gfx90a gfx90c gfx1010 gfx1030 gfx1031)
 if (DEFINED LIBOMPTARGET_AMDGCN_GFXLIST)
   set(amdgpu_mcpus ${LIBOMPTARGET_AMDGCN_GFXLIST})
 endif()
 
 
 # Activate RTL message dumps if requested by the user.
 set(LIBOMPTARGET_DEVICE_DEBUG FALSE CACHE BOOL
   "Activate DeviceRTL debug messages.")