[clang] Optimize storage and lookup of analyzer options

[jansvoboda11]

Summary

This patch removes std::vector, std::sort() and std::binary_search() in AnalyzerOptions with a static llvm::StringSwitch.

This avoids unnecessary work, which can speed up Clang tools that initialize lots of CompilerInvocations (and therefore AnalyzerOptions).

[steakhal]

Are you sure about the speedup?
When I looked at the implementation of the StringSwitch, it boiled down to an if-else chain under the hood.

[steakhal]

BTW the change itself looks good to me.

[jansvoboda11]

In D137258#3947181, @steakhal wrote:

Are you sure about the speedup?
When I looked at the implementation of the StringSwitch, it boiled down to an if-else chain under the hood.

You're right. I assumed StringSwitch was more sophisticated than that. This patch provides speedup for my use-case, which involves constructing lots of AnalyzerOptions instances, but no calls to AnalyzerOptions::isUnknownAnalyzerConfig(). I'll spend more time on this and make sure I don't regress the lookup. (Unfortunately, std::sort is only constexpr in C++20 onwards, so I can't just sort the options at compile-time.)