[llvm] [llvm]Add a simple Telemetry framework (PR #102323)

[Vy Nguyen via llvm-commits]

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+===========================
+Telemetry framework in LLVM
+===========================
+
+.. contents::
+   :local:
+
+.. toctree::
+   :hidden:
+
+===========================
+Telemetry framework in LLVM
+===========================
+
+Objective
+=========
+
+Provides a common framework in LLVM for collecting various usage and performance
+metrics.
+It is located at `llvm/Telemetry/Telemetry.h`
+
+Characteristics
+---------------
+* Configurable and extensible by:
+
+  * Tools: any tool that wants to use Telemetry can extend and customize it.
+  * Vendors: Toolchain vendors can also provide custom implementation of the
+    library, which could either override or extend the given tool's upstream
+    implementation, to best fit their organization's usage and privacy models.
+  * End users of such tool can also configure Telemetry (as allowed by their
+    vendor).
+
+
+Important notes
+----------------
+
+* There is no concrete implementation of a Telemetry library in upstream LLVM.
+  We only provide the abstract API here. Any tool that wants telemetry will
+  implement one.
+  
+  The rationale for this is that, all the tools in LLVM are very different in
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oontvoo wrote:

done.

https://github.com/llvm/llvm-project/pull/102323