[clang] [CIR] Enable x86_64 calling-convention lowering by default (PR #215026)

[Andy Kaylor via cfe-commits]

================
@@ -423,9 +423,10 @@ class FrontendOptions {
   LLVM_PREFERRED_TYPE(bool)
   unsigned ClangIREnableIdiomRecognizer : 1;
 
-  /// Enable Clang IR (CIR) calling-convention lowering
+  /// Run the Clang IR (CIR) calling-convention lowering pass.  A no-op on
+  /// targets whose calling convention is not yet implemented.
   LLVM_PREFERRED_TYPE(bool)
-  unsigned ClangIREnableCallConvLowering : 1;
+  unsigned ClangIRCallConvLowering : 1;
----------------
andykaylor wrote:

We're terribly inconsistent about the naming of these options -- `ClangIREnableIdiomRecognizer`, `ClangIRCallConvLowering`, `ClangIRLibOptEnabled`. The old name here was at least consistent with one of the other two. Can we standardize on that naming scheme?

https://github.com/llvm/llvm-project/pull/215026