[NFC] Use hasSection instead of getSection().empty()

Use the optimized check hasSection() instead of calling
getSection().empty(). Originally suggested in D101004, but was dropped
in the commit.

llvm/lib/CodeGen/MachineFunctionSplitter.cpp

@@ -101,7 +101,7 @@ bool MachineFunctionSplitter::runOnMachineFunction(MachineFunction &MF) {
   // since the split part may not be placed in a contiguous region. It may also
   // be more beneficial to augment the linker to ensure contiguous layout of
   // split functions within the same section as specified by the attribute.
-  if (!MF.getFunction().getSection().empty() ||
+  if (MF.getFunction().hasSection() ||
       MF.getFunction().hasFnAttribute("implicit-section-name"))
     return false;