[llvm] [APFloat] Add exp function for APFloat::IEEESsingle using expf implementation from LLVM libc. (PR #143959)

[Michael Jones via llvm-commits]

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@@ -644,6 +644,17 @@ endif()
 
 set(LLVM_ENABLE_Z3_SOLVER_DEFAULT "${Z3_FOUND}")
 
+set(LLVM_INTEGRATE_LIBC "OFF" CACHE STRING "Use LLVM libc codes directly if available.")
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michaelrj-google wrote:

nit: 
```suggestion
set(LLVM_INTEGRATE_LIBC "OFF" CACHE STRING "Use LLVM libc code directly if available.")
```

https://github.com/llvm/llvm-project/pull/143959