runtime(dosini): save and restore cpo value in syntax script #4

Job	Run time
macos (tiny)	1m 52s
macos (normal)	16m 4s
macos (huge)	15m 22s
windows (HUGE, msvc, no, no, x64, stable)	8m 31s
windows (HUGE, mingw, yes, yes, x86, stable, yes)	12m 54s
windows (HUGE, msvc, no, yes, x86)	9m 18s
windows (HUGE, mingw, yes, no, x64, yes)	11m 23s
windows (NORMAL, msvc, yes, no, x86)	8m 5s
windows (NORMAL, mingw, no, yes, x64)	10m 37s
windows (TINY, msvc, yes, yes, x64)	2m 30s
windows (TINY, mingw, no, no, x86)	3m 25s
linux (tiny, clang, none, lua5.4)	4m 35s
linux (tiny, gcc, none, lua5.4)	2m 35s
linux (normal, clang, none, lua5.4)	9m 52s
linux (normal, gcc, none, lua5.4)	9m 2s
linux (huge, clang, none, lua5.4)	9m 29s
linux (huge, gcc, none, lua5.4)	15m 37s
linux (tiny, clang, nogui)	2m 14s
linux (tiny, gcc, nogui)	1m 38s
linux (huge, gcc, testgui, lua5.4, true, dynamic, true)	12m 14s
linux (huge, clang, asan, lua5.1)	25m 55s
linux (huge, gcc, unittests, lua5.4, true)	3m 40s
linux (normal, gcc, vimtags)	1m 24s
	3h 18m 16s

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