Use Clang rather than GCC for assembly. (#2377) #6457

Job	Run time
find-languages	3s
bare-metal (src/bare-metal/alloc-example, aarch64-unknown-none)	37s
cargo (ubuntu-latest)	30s
bare-metal (src/bare-metal/aps/examples, aarch64-unknown-none)	25s
format	35s
cargo (macos-latest)	29s
Translation diff	2m 15s
bare-metal (src/bare-metal/microcontrollers/examples, thumbv7em-none-eabihf)	1m 2s
bare-metal (src/exercises/bare-metal/compass, thumbv7em-none-eabihf)	44s
typos	6s
bare-metal (src/exercises/bare-metal/rtc, aarch64-unknown-none)	42s
build (ar)	4m 40s
build (bn)	4m 49s
build (da)	4m 29s
build (de)	5m 4s
build (el)	5m 20s
build (en)	3m 23s
build (es)	4m 54s
build (fa)	4m 6s
build (fr)	4m 47s
build (id)	4m 32s
build (it)	4m 54s
build (ja)	6m 16s
build (ko)	6m 1s
build (pl)	4m 21s
build (pt-BR)	4m 28s
build (ro)	4m 30s
build (ru)	4m 59s
build (tr)	5m 3s
build (uk)	4m 23s
build (vi)	4m 34s
build (zh-CN)	5m 50s
build (zh-TW)	5m 38s
	1h 54m 29s

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