[M68k] Use `softPromoteHalfType` (#175140)

Follow suite from other targets.

Fixes the M68k portion of
https://github.com/llvm/llvm-project/issues/97975
Fixes the M68k portion of
https://github.com/llvm/llvm-project/issues/97981

llvm/lib/Target/M68k/M68kISelLowering.h

diff --git a/llvm/lib/Target/M68k/M68kISelLowering.h b/llvm/lib/Target/M68k/M68kISelLowering.h
index 3774f93..b7e3dd7 100644
--- a/llvm/lib/Target/M68k/M68kISelLowering.h
+++ b/llvm/lib/Target/M68k/M68kISelLowering.h
@@ -253,6 +253,8 @@
       const SmallVectorImpl<ISD::InputArg> &Ins, SelectionDAG &DAG) const;
 
   SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const override;
+
+  bool softPromoteHalfType() const override { return true; }
 };
 } // namespace llvm
 

llvm/test/CodeGen/Generic/half-op.ll

diff --git a/llvm/test/CodeGen/Generic/half-op.ll b/llvm/test/CodeGen/Generic/half-op.ll
index 5648820..45df0c4a 100644
--- a/llvm/test/CodeGen/Generic/half-op.ll
+++ b/llvm/test/CodeGen/Generic/half-op.ll
@@ -20,7 +20,7 @@
 ; RUN: %if loongarch-registered-target   %{ llc %s -o - -mtriple=loongarch32-unknown-linux-gnu   | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
 ; RUN: %if loongarch-registered-target   %{ llc %s -o - -mtriple=loongarch64-unknown-linux-gnu   | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
 ; RUN: %if loongarch-registered-target   %{ llc %s -o - -mtriple=loongarch64-unknown-linux-gnu -mattr=+f | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
-; RUN: %if m68k-registered-target        %{ llc %s -o - -mtriple=m68k-unknown-linux-gnu          | FileCheck %s --check-prefixes=ALL,BAD-NEG-ABS,BAD-COPYSIGN,BAD-FMA %}
+; RUN: %if m68k-registered-target        %{ llc %s -o - -mtriple=m68k-unknown-linux-gnu          | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
 ; RUN: %if mips-registered-target        %{ llc %s -o - -mtriple=mips-unknown-linux-gnu          | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
 ; RUN: %if mips-registered-target        %{ llc %s -o - -mtriple=mips64-unknown-linux-gnuabi64   | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}
 ; RUN: %if mips-registered-target        %{ llc %s -o - -mtriple=mips64el-unknown-linux-gnuabi64 | FileCheck %s --check-prefixes=ALL,CHECK-NEG-ABS,CHECK-COPYSIGN,CHECK-FMA %}