Improve diagnostic for attempt to use `get_name` with non-external #293

Job	Run time
windows (msvc-14.0, 14,latest, 32,64, windows-2019, -j3)	1m 23s
posix (gcc-12, 03,11,14,17,2a, ubuntu-22.04, cxxflags=--coverage -fsanitize=address,leak,undefine...	7m 44s
windows (gcc, 03,11,14,17,2a, 64, windows-2019, -j3)	7m 1s
posix (gcc-11, 03,11,14,17,2a, ubuntu-22.04, cxxflags=--coverage -fsanitize=address,leak,undefine...	8m 31s
windows (msvc-14.3, 20,latest, 64, windows-2022, -j1)	14m 0s
posix (gcc-10, 03,11,14,17,2a, ubuntu-22.04, cxxflags=--coverage -fsanitize=address,leak,undefine...	7m 32s
posix (gcc-9, 03,11,14,17,2a, ubuntu-22.04, cxxflags=--coverage -fsanitize=address,leak,undefined...	6m 13s
posix (clang-14, 03,11,14,17,20, ubuntu-22.04)	6m 24s
posix (clang-13, 03,11,14,17,20, ubuntu-22.04)	6m 38s
finish	0s
	1h 5m 26s

Provide feedback