Use Shallow Submodule Init to Reduce Clone Times #544

Job	Run time
test-sim (ubuntu-24.04, newlib, rv64gc-lp64d, spike)	2h 35m 29s
build (ubuntu-22.04, newlib, rv32gc-ilp32d, gcc)	42m 48s
build-multilib	0s
build (ubuntu-22.04, newlib, rv32gc-ilp32d, llvm)	1h 59m 3s
build (ubuntu-22.04, newlib, rv64gc-lp64d, gcc)	43m 55s
build (ubuntu-22.04, newlib, rv64gc-lp64d, llvm)	2h 1m 49s
build (ubuntu-22.04, linux, rv32gc-ilp32d, gcc)	50m 15s
build (ubuntu-22.04, linux, rv32gc-ilp32d, llvm)	2h 6m 42s
build (ubuntu-22.04, linux, rv64gc-lp64d, gcc)	50m 57s
build (ubuntu-22.04, linux, rv64gc-lp64d, llvm)	2h 16m 7s
build (ubuntu-22.04, musl, rv32gc-ilp32d, gcc)	42m 33s
build (ubuntu-22.04, musl, rv64gc-lp64d, gcc)	43m 16s
build (ubuntu-22.04, uclibc, rv32gc-ilp32d, gcc)	5m 8s
build (ubuntu-22.04, uclibc, rv64gc-lp64d, gcc)	3m 57s
build (ubuntu-24.04, newlib, rv32gc-ilp32d, gcc)	2h 14m 6s
build (ubuntu-24.04, newlib, rv32gc-ilp32d, llvm)	2h 14m 29s
build (ubuntu-24.04, newlib, rv64gc-lp64d, gcc)	2h 15m 32s
build (ubuntu-24.04, newlib, rv64gc-lp64d, llvm)	2h 16m 40s
build (ubuntu-24.04, linux, rv32gc-ilp32d, gcc)	3h 10m 52s
build (ubuntu-24.04, linux, rv32gc-ilp32d, llvm)	2h 25m 9s
build (ubuntu-24.04, linux, rv64gc-lp64d, gcc)	3h 15m 36s
build (ubuntu-24.04, linux, rv64gc-lp64d, llvm)	2h 27m 20s
build (ubuntu-24.04, musl, rv32gc-ilp32d, gcc)	46m 50s
build (ubuntu-24.04, musl, rv64gc-lp64d, gcc)	48m 18s
build (ubuntu-24.04, uclibc, rv32gc-ilp32d, gcc)	2m 39s
build (ubuntu-24.04, uclibc, rv64gc-lp64d, gcc)	2m 27s
	1d 13h 41m 57s

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