[llvm] [RISCV] Use consume_front to parse rv32/rv64 in RISCVISAInfo::parse*ArchString. NFC (PR #90562)

[Craig Topper via llvm-commits]

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@@ -616,36 +616,39 @@ RISCVISAInfo::parseArchString(StringRef Arch, bool EnableExperimentalExtension,
                            ExperimentalExtensionVersionCheck, IgnoreUnknown);
   }
 
-  bool HasRV64 = Arch.starts_with("rv64");
   // ISA string must begin with rv32 or rv64.
-  if (!(Arch.starts_with("rv32") || HasRV64) || (Arch.size() < 5)) {
+  unsigned XLen = 0;
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topperc wrote:

Might be worth making this into a subroutine to share.

https://github.com/llvm/llvm-project/pull/90562