[stdlib] Remove invalid _sanityCheck

[dabrahams]

A Character should contain only a single grapheme, but we can't formally require it because of grapheme cluster literals and the shifting sands of Unicode. Fixes https://bugs.swift.org/browse/SR-4955

Note: the stray change in the comment is due to GitHub's editor changing all text from decomposed to precomposed.

[dabrahams]

@swift-ci Please smoke test and merge

[palimondo]

This indeed fixed SR-4955 on my machine.
I don't understand why was only I affected… My configuration should be normal AFAIK: build-script -R. Are there some processor specific optimizations involved somewhere? Only atypical thing is that I'm running on 8 years old Core 2 duo here…

[gottesmm]

@palimondo The issue is that our normal perf test run builds without assertions. This was caught by a different bot that we have internally that builds the perf test with assertions. I could move it externally, I just have not gotten around to it.

[palimondo]

@gottesman And the perf-test I get locally out of build-script -R is with assertions?

[gottesmm]

@palimondo Did you do a clean build? If not, look in your build directory for CMakeCache.txt and see what SWIFT_STDLIB_ASSERTIONS is set to. Reconfigs sometimes can cause that value to get out of sync.

[palimondo]

Um... clean build, when? I have never adjusted assertions AFAIK. I did clean build
(by deleting contests of build directory) when SR-4955 was failing for me. IIRC it looks like Dave was able to reproduce my error on a build with assertions and discovered the invalid _sanityCheck. What I don’t understand how/why I stumbled upon this and how it only manifested on my machine.

[palimondo]

@gottesmm While I have your ear... I wrote you an email with request for guidance re: tests and modularization of Benchmark_Driver. Could you respond, plz?

[gottesmm]

I saw your email. It was a long email, so the response took some thoughts. I kept on getting pulled into things over the weekend so I was unable to. I will finish responding later today.