[clang] [clang] Enable constexpr handling for __builtin_elementwise_fma (PR #152919)

[Chaitanya Koparkar via cfe-commits]

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@@ -11,3 +11,55 @@ float V3 = func_01(1.0F, 2.0F);
 // CHECK: @V1 = {{.*}}global float 1.000000e+00, align 4
 // CHECK: @V2 = {{.*}}global float 1.000000e+00, align 4
 // CHECK: @V3 = {{.*}}global float 3.000000e+00, align 4
+
+void test_builtin_elementwise_fma_round_upward() {
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ckoparkar wrote:

@arsenm Tests for different rounding modes. I chose this file rather than `constant-builtins-vector.cpp` because, it's already testing rounding modes and already has the appropriate `RUN`  command set up.

https://github.com/llvm/llvm-project/pull/152919