Support no_std integration tests #2340

Job	Run time
msrv	2m 8s
rustfmt	6s
miri-regex-automata	10m 10s
test (stable, ubuntu-latest, stable)	3m 44s
testfull-regex	3m 47s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 35s
testfull-regex-automata	8m 48s
testfull-regex-capi	22s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 29s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	8m 44s
testfull-regex-syntax	2m 8s
test (beta, ubuntu-latest, beta)	3m 57s
test (nightly, ubuntu-latest, nightly)	3m 11s
test (macos, macos-latest, stable)	2m 25s
test (win-msvc, windows-latest, stable)	6m 35s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 50s
	1h 9m 59s

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