[AArch64][GlobalISel] Legalize G_INTRINSIC_TRUNC

Same patch as G_FCEIL etc.

Add the missing switch case in widenScalar, add G_INTRINSIC_TRUNC to the correct
rule in AArch64LegalizerInfo.cpp, and add a test.

llvm-svn: 359021
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 4b592b3..9521e67 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -1327,6 +1327,7 @@
   case TargetOpcode::G_FEXP:
   case TargetOpcode::G_FEXP2:
   case TargetOpcode::G_FPOW:
+  case TargetOpcode::G_INTRINSIC_TRUNC:
     assert(TypeIdx == 0);
     Observer.changingInstr(MI);