watch: re-expose watch flags via execArgv #799

Job	Run time
Build slim tarball	1m 32s
aarch64-linux: with shared libraries	24m 33s
x86_64-darwin: with shared libraries	35m 22s
aarch64-darwin: with shared libraries	27m 52s
x86_64-linux: with shared libraries	28m 2s
	1h 57m 21s

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