Add support for x86_64-pc-windows-gnullvm #479

Job	Run time
Rustfmt	13s
Test (x86_64-unknown-linux-gnu, stable, ubuntu-latest)	6m 28s
Test (x86_64-unknown-linux-gnu, beta, ubuntu-latest)	6m 26s
Test (x86_64-unknown-linux-gnu, nightly, ubuntu-latest)	6m 19s
Test (x86_64-apple-darwin, stable, macos-latest)	2m 1s
Test (aarch64-apple-darwin, nightly, macos-latest)	2m 43s
Test (i686-unknown-linux-gnu, stable, ubuntu-latest)	3m 31s
Test (arm-unknown-linux-gnueabi, stable, ubuntu-latest)	3m 28s
Test (aarch64-unknown-linux-gnu, stable, ubuntu-latest)	3m 40s
Test (riscv64gc-unknown-linux-gnu, stable, ubuntu-latest)	3m 35s
Test (x86_64-unknown-linux-musl, stable, ubuntu-latest)	3m 8s
Test (x86_64-pc-windows-gnu, stable, ubuntu-latest)	7m 51s
Test (i686-pc-windows-msvc, stable-i686-msvc, windows-2019)	19m 54s
Test (i686-pc-windows-msvc, stable-i686-msvc, windows-2019, yes)	19m 50s
Test (x86_64-pc-windows-msvc, stable-x86_64-msvc, windows-latest)	20m 5s
Test (x86_64-pc-windows-msvc, stable-x86_64-msvc, windows-latest, yes)	18m 57s
Test (x86_64-pc-windows-msvc, stable-x86_64-msvc, windows-latest, installed)	19m 56s
	2h 28m 5s

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