[clang-tools-extra] [clangd] Introduce --skip-preamble-build command line option (PR #189284)

[Aleksandr Platonov via cfe-commits]

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@@ -525,6 +525,14 @@ opt<bool> PreambleParseForwardingFunctions{
     init(ParseOptions().PreambleParseForwardingFunctions),
 };
 
+opt<bool> SkipPreambleBuild{
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ArcsinX wrote:

With this option we control preamble optimization.  So, maybe "PreambleOptimization" with default `true` value can be more clear.
I want to avoid using "PCH" in this option name, since this relates to the implementation details of preamble optimization.

https://github.com/llvm/llvm-project/pull/189284