[llvm] Reland "[APFloat] Add exp functions for single and double using exp/expf implementations from LLVM libc." (#197440) (PR #199570)

[Danila Malyutin via llvm-commits]

================
@@ -399,7 +399,12 @@ endif()
 target_include_directories(LLVMSupport
   PRIVATE
   ${LLVM_THIRD_PARTY_DIR}/siphash/include
+  ${LLVM_SOURCE_DIR}/../libc
----------------
danilaml wrote:

Who sets the `LLVM_SOURCE_DIR`? Shouldn't it be `LLVM_MAIN_SRC_DIR`?

https://github.com/llvm/llvm-project/pull/199570