Make dependency trackers async + assorted minor improvements #277

Job	Run time
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, ON, Debug, none)	2m 13s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, ON, Debug, asan)	3m 46s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, ON, Release, none)	2m 23s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, ON, Release, asan)	1h 4m 51s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, OFF, Debug, none)	2m 7s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, OFF, Debug, asan)	3m 38s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, OFF, Release, none)	2m 17s
build (/opt/gcc-12.4/bin/gcc;/opt/gcc-12.4/bin/g++;/opt/gcc-12.4/lib64, OFF, Release, asan)	1h 4m 31s
build (clang;clang++;, ON, Debug, none)	2m 8s
build (clang;clang++;, ON, Debug, asan)	2m 36s
build (clang;clang++;, ON, Release, none)	2m 7s
build (clang;clang++;, ON, Release, asan)	3m 51s
build (clang;clang++;, OFF, Debug, none)	2m 3s
build (clang;clang++;, OFF, Debug, asan)	2m 31s
build (clang;clang++;, OFF, Release, none)	2m 2s
build (clang;clang++;, OFF, Release, asan)	3m 42s
	2h 46m 46s

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