Support -Zforce-intrinsic-fallback #1878

Job	Run time
abi_cafe (macos-latest, aarch64-apple-darwin)	5m 49s
abi_cafe (macos-15-intel, x86_64-apple-darwin)	12m 33s
abi_cafe (ubuntu-latest, x86_64-unknown-linux-gnu)	6m 58s
abi_cafe (ubuntu-24.04-arm, aarch64-unknown-linux-gnu)	5m 52s
abi_cafe (windows-latest, x86_64-pc-windows-msvc)	9m 43s
	40m 55s

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