[clang] [llvm] [AMDGPU] Implement 'llvm.get.fpenv' and 'llvm.set.fpenv' (PR #83906)

[Matt Arsenault via cfe-commits]

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@@ -839,6 +839,18 @@ unsigned test_wavefrontsize() {
   return __builtin_amdgcn_wavefrontsize();
 }
 
+// CHECK-LABEL test_get_fpenv(
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arsenm wrote:

Ideally we would also warn if you used these without fenv access enabled 

https://github.com/llvm/llvm-project/pull/83906