Share environment code between exe and sh backend (WIP) #236

Job	Run time
bootstrap-pnut-sh-with-pnut-exe (i386_linux)	12s
bootstrap-pnut-sh (bash)	1m 19s
bootstrap-pnut-sh-with-pnut-exe (x86_64_linux)	12s
bootstrap-pnut-sh (dash)	1m 46s
bootstrap-pnut-sh-with-pnut-exe (x86_64_mac)	16s
bootstrap-pnut-sh (ksh)	41s
build-without-warnings	11s
bootstrap-pnut-sh (mksh)	12m 54s
bootstrap-pnut-sh (yash)	1m 18s
bootstrap-pnut-sh (zsh)	11m 0s
catch-bad-whitespace	4s
tests-exe (i386_linux, ubuntu-latest)	10s
tests-shell (bash)	13s
tests-exe (x86_64_linux, ubuntu-latest)	9s
tests-shell (dash)	19s
bootstrap-bash-2_05a	20m 46s
tests-exe (x86_64_mac, macos-latest)	11s
tests-shell (ksh)	17s
tests-shell (mksh)	1m 7s
tests-shell (yash)	48s
bootstrap-pnut-exe (bash, i386_linux)	42s
tests-shell (zsh)	19s
bootstrap-pnut-exe (bash, x86_64_linux)	42s
bootstrap-pnut-exe (bash, x86_64_mac)	41s
bootstrap-pnut-exe (dash, i386_linux)	41s
bootstrap-pnut-exe (dash, x86_64_linux)	37s
bootstrap-pnut-exe (dash, x86_64_mac)	41s
bootstrap-pnut-exe (ksh, i386_linux)	28s
bootstrap-pnut-exe (ksh, x86_64_linux)	36s
bootstrap-pnut-exe (ksh, x86_64_mac)	17s
success-message	0s
	59m 37s

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