[clang] [flang] [llvm] Introduce -fexperimental-loop-fuse to clang and flang (PR #142686)

[Fangrui Song via llvm-commits]

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@@ -4268,6 +4268,10 @@ def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
   HelpText<"Enable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>,
   HelpText<"Disable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
+def fexperimental_loop_fusion : Flag<["-"], "fexperimental-loop-fusion">, Group<f_Group>,
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MaskRay wrote:

We can use `OptInCC1FFlag` so that the negative form is not a `clang -cc1` option.

https://github.com/llvm/llvm-project/pull/142686