Add: Support wasm32-unknown-emscripten #3330

Job	Run time
features_check (ubuntu-latest)	5m 27s
rust_msrv (ubuntu-latest)	57s
rust_versions (ubuntu-latest, stable)	1m 4s
rust_versions (ubuntu-latest, beta)	1m 4s
timezones (ubuntu-latest, ACST-9:30)	1m 19s
rust_versions (ubuntu-latest, nightly)	1m 4s
timezones (ubuntu-latest, EST4)	1m 18s
timezones (ubuntu-latest, UTC0)	1m 19s
timezones (ubuntu-latest, Asia/Katmandu)	1m 13s
timezones (macos-latest, ACST-9:30)	1m 16s
timezones (macos-latest, EST4)	1m 0s
timezones (macos-latest, UTC0)	55s
timezones (macos-latest, Asia/Katmandu)	54s
timezones (windows-latest, ACST-9:30)	1m 26s
timezones (windows-latest, EST4)	1m 29s
timezones (windows-latest, UTC0)	1m 34s
alternative_targets (ubuntu-latest, wasm32-unknown-emscripten)	39s
timezones (windows-latest, Asia/Katmandu)	1m 25s
alternative_targets (ubuntu-latest, aarch64-apple-ios)	30s
alternative_targets (ubuntu-latest, aarch64-linux-android)	18s
check-docs	25s
cross-targets (x86_64-unknown-illumos)	1m 13s
cross-tests (ubuntu-latest)	1m 53s
test_emscripten (ubuntu-latest)	45s
test_wasi (ubuntu-latest, wasm32-wasi)	24s
no_std (ubuntu-latest, thumbv6m-none-eabi)	15s
test_wasm (ubuntu-latest)	22s
no_std (ubuntu-latest, x86_64-fortanix-unknown-sgx)	20s
	31m 48s

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