Dependency to libICU should be optional

[WojciechMula]

Didn't dig into the benchmarks' details, but I believe me may conditionally compile parts requiring ICU.

[lemire]

@WojciechMula I think that it is currently optional in the sense that it should still build even if ICU is missing.

Of course, it would be nicer to build it as a CMake dependency, say.

(Be mindful that we want to be as portable as possible.)

[lemire]

Also, of course, it is only required for benchmarking.

[WojciechMula]

Unfortunately, the lib does not build if ICU is missing. I'll look at this in my spare time.

[lemire]

That's a bug because we do have the checks in place...

simdutf/benchmarks/src/benchmark.h

Line 58 in 98915f8

#if ICU_AVAILABLE

[WojciechMula]

Sorry, it was my mistake. Cmake reported an error, but I didn't notice that I pasted some garbage into the cmd line. The actual error wasn't related to ICU.