[CodeGen] Inline trivial TargetLoweringBase::getCmpLibcallReturnType method. NFC (#192483)

This trivial method makes more sense in the header (indeed, both the
existing overrides for it are already in headers).

I noticed this while hunting for the default value while reviewing
#192425

Author: sbc100

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -996,8 +996,9 @@ class LLVM_ABI TargetLoweringBase {
   /// Return the ValueType for comparison libcalls. Comparison libcalls include
   /// floating point comparison calls, and Ordered/Unordered check calls on
   /// floating point numbers.
-  virtual
-  MVT::SimpleValueType getCmpLibcallReturnType() const;
+  virtual MVT::SimpleValueType getCmpLibcallReturnType() const {
+    return MVT::i32; // return the default value
+  }
 
   /// For targets without i1 registers, this gives the nature of the high-bits
   /// of boolean values held in types wider than i1.

llvm/lib/CodeGen/TargetLoweringBase.cpp

@@ -1959,10 +1959,6 @@ EVT TargetLoweringBase::getSetCCResultType(const DataLayout &DL, LLVMContext &,
   return getPointerTy(DL).SimpleTy;
 }
 
-MVT::SimpleValueType TargetLoweringBase::getCmpLibcallReturnType() const {
-  return MVT::i32; // return the default value
-}
-
 /// getVectorTypeBreakdown - Vector types are broken down into some number of
 /// legal first class types.  For example, MVT::v8f32 maps to 2 MVT::v4f32
 /// with Altivec or SSE1, or 8 promoted MVT::f64 values with the X86 FP stack.