[MC] Port initializeVariantKinds to ARM COFF and SystemZ GOFF

... so that they use the target-specific variantKindDescs instead of the
generic MCExpr one (which will go away as it's error-prone).

Author: MaskRay

llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp

@@ -129,6 +129,8 @@ ARMCOFFMCAsmInfoMicrosoft::ARMCOFFMCAsmInfoMicrosoft() {
 
   // Conditional Thumb 4-byte instructions can have an implicit IT.
   MaxInstLength = 6;
+
+  initializeVariantKinds(variantKindDescs);
 }
 
 void ARMCOFFMCAsmInfoGNU::anchor() { }

llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmInfo.cpp

@@ -53,6 +53,8 @@ SystemZMCAsmInfoGOFF::SystemZMCAsmInfoGOFF(const Triple &TT) {
   IsLittleEndian = false;
   MaxInstLength = 6;
   SupportsDebugInformation = true;
+
+  initializeVariantKinds(variantKindDescs);
 }
 
 bool SystemZMCAsmInfoGOFF::isAcceptableChar(char C) const {