[libc] add back math.h #include utils/FPUtil/ManipulationFunctions.h

This partially reverts cee1e7d1:
  [libc][NFC][Obvious] Remove few unnecessary #include directives in tests.

That commit causes a test failure in our configuration:
[ RUN      ] ILogbTest.SpecialNumbers_ilogb
third_party/llvm/llvm-project/libc/test/src/math/ILogbTest.h:28: FAILURE
      Expected: FP_ILOGBNAN
      Which is: 2147483647
To be equal to: func(__llvm_libc::fputil::FPBits<T>::buildNaN(1))
      Which is: -2147483648