[libclc] [libclc] Move mad to the CLC library (PR #123607)

[Matt Arsenault via cfe-commits]

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@@ -0,0 +1,4 @@
+_CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_mad(__CLC_GENTYPE a, __CLC_GENTYPE b,
+                                               __CLC_GENTYPE c) {
+  return a * b + c;
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arsenm wrote:

probably should use the pragma to explicitly allow contract 

https://github.com/llvm/llvm-project/pull/123607