[llvm] [Docs][llvm-exegesis] Clarify AArch64 support (PR #114989)

[Aiden Grossman via llvm-commits]

================
@@ -33,11 +33,13 @@ snippets.
 SUPPORTED PLATFORMS
 -------------------
 
-:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM (AArch64
-only), MIPS, and PowerPC (PowerPC64LE only) on Linux for benchmarking. Not all
-benchmarking functionality is guaranteed to work on every platform.
-:program:`llvm-exegesis` also has a separate analysis mode that is supported
-on every platform that LLVM is.
+:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM
+(AArch64 only and very experimental), MIPS, and PowerPC (PowerPC64LE only) on
----------------
boomanaiden154 wrote:

I would explicitly state here that snippet generation is experimental. In process snippet execution should "just work".

Maybe something like "AArch64 only, snippet generation support is sparse".

https://github.com/llvm/llvm-project/pull/114989