runtime(dosini): save and restore cpo value in syntax script #1

Job	Run time
macos (tiny)	3m 36s
macos (normal)	9m 18s
macos (huge)	14m 19s
windows (HUGE, msvc, no, no, x64, stable)	8m 16s
windows (HUGE, mingw, yes, yes, x86, stable, yes)	16m 18s
windows (HUGE, msvc, no, yes, x86)	9m 24s
windows (HUGE, mingw, yes, no, x64, yes)	14m 9s
windows (NORMAL, msvc, yes, no, x86)	7m 14s
windows (NORMAL, mingw, no, yes, x64)	11m 49s
windows (TINY, msvc, yes, yes, x64)	3m 21s
windows (TINY, mingw, no, no, x86)	5m 13s
linux (tiny, clang, none, lua5.4)	2m 42s
linux (tiny, gcc, none, lua5.4)	2m 39s
linux (normal, clang, none, lua5.4)	10m 11s
linux (normal, gcc, none, lua5.4)	10m 3s
linux (huge, clang, none, lua5.4)	8m 53s
linux (huge, gcc, none, lua5.4)	17m 56s
linux (tiny, clang, nogui)	2m 9s
linux (tiny, gcc, nogui)	1m 42s
linux (huge, gcc, testgui, lua5.4, true, dynamic, true)	11m 31s
linux (huge, clang, asan, lua5.1)	28m 0s
linux (huge, gcc, unittests, lua5.4, true)	3m 9s
linux (normal, gcc, vimtags)	1m 58s
	3h 23m 50s

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