Cycles: oneAPI: Re-enable -ffast-math

The initial limitation preventing from using -ffast-math, worked around
in 09df1f4caf, got fixed upstream in LLVM
and the fix is part of current DPC++ compiler:
63ecd2a725

We're now able to go back to using -ffast-math, which helps simplifying
the set of compiler flags.

No performance nor conformance change is expected from this change (most
of the gain is achieved already with the use of -cl-fast-relaxed-math
since 284b89a0a3) and this has been
verified on Arc B580 under Windows.

intern/cycles/kernel/CMakeLists.txt

@@ -968,12 +968,7 @@ if(WITH_CYCLES_DEVICE_ONEAPI)
     -shared
     -DWITH_ONEAPI
     -O2
-    -fno-fast-math
-    -ffp-contract=fast
-    -fassociative-math
-    -freciprocal-math
-    -fno-signed-zeros
-    -ffinite-math-only
+    -ffast-math
     -D__KERNEL_LOCAL_ATOMIC_SORT__
     -o"${cycles_kernel_oneapi_lib}"
     -I"${CMAKE_CURRENT_SOURCE_DIR}/.."