win/spawn: optionally run executable paths with no file extension (#4… #5

Job	Run time
build-ios	1m 47s
build-linux	1m 35s
build-macos	3m 39s
build-android	2m 22s
build-cross-qemu-arm	1m 43s
build-cross-qemu-armhf	1m 40s
build-cross-qemu-aarch64	1m 39s
build-cross-qemu-riscv64	1m 30s
build-cross-qemu-ppc	1m 48s
build-cross-qemu-ppc64	1m 37s
build-cross-qemu-ppc64le	1m 34s
build-cross-qemu-s390x	1m 36s
build-cross-qemu-mips	1m 41s
build-cross-qemu-mips64	1m 33s
build-cross-qemu-mipsel	1m 51s
build-cross-qemu-mips64el	1m 43s
build-cross-qemu-arm (u64 slots)	1m 31s
build-cross-qemu-aarch64 (u64 slots)	2m 22s
build-cross-qemu-ppc (u64 slots)	2m 19s
build-cross-qemu-ppc64 (u64 slots)	1m 46s
	37m 16s

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