Note special status of R12 in x86_64 jitter #992

Job	Run time
linux_debug_coverage / build	1m 20s
linux_debug_arm64 / build	2m 41s
linux_debug_arm64_coverage / build	2m 39s
linux_debug / build	59s
linux_debug_sanitizers / build	1m 7s
linux_release / build	55s
linux_release_arm64 / build	2m 30s
linux_release_arm64_coverage / build	2m 11s
linux_release_coverage / build	1m 6s
linux_release_sanitizers / build	1m 13s
macos_debug / build	3m 30s
linux_release_scan_build / build	1m 46s
macos_debug_coverage / build	4m 1s
macos_debug_sanitizers / build	4m 39s
macos_release / build	3m 10s
macos_release_coverage / build	3m 42s
macos_release_sanitizers / build	4m 16s
windows_debug / build	4m 28s
windows_release / build	5m 59s
finish	0s
	52m 12s

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