re2c: Disable UTF-8 #312

Job	Run time
linter	1m 21s
windows (shared)	1m 51s
posix (linux, clang, shared)	30s
windows (static)	4m 34s
posix (linux, clang, shared, ASan)	43s
posix (linux, clang, static)	1m 47s
posix (linux, clang, static, ASan)	1m 2s
posix (linux, gcc, shared)	1m 6s
posix (linux, gcc, shared, ASan)	18s
posix (linux, gcc, static)	8s
posix (linux, gcc, static, ASan)	1m 9s
posix (macos, clang, shared)	1m 13s
posix (macos, clang, static)	19s
posix (macos, clang, static, ASan)	2m 10s
	18m 11s

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