[SpaceEngine] NFC: Switch to != instead of compare on Head identifiers

Since `Head` comparison only checks for equality, all of such
checks could be switched from `compare` to `!=` operator.

Author: xedin

lib/Sema/TypeCheckSwitchStmt.cpp

@@ -404,7 +404,7 @@ namespace {
         PAIRCASE (SpaceKind::Constructor, SpaceKind::Constructor): {
           // Optimization: If the constructor heads don't match, subspace is
           // impossible.
-          if (this->Head.compare(other.Head) != 0) {
+          if (this->Head != other.Head) {
             return false;
           }
 
@@ -551,7 +551,7 @@ namespace {
         PAIRCASE (SpaceKind::Constructor, SpaceKind::Constructor): {
           // Optimization: If the heads don't match, the intersection of
           // the constructor spaces is empty.
-          if (this->getHead().compare(other.Head) != 0) {
+          if (this->getHead() != other.Head) {
             return Space();
           }
 
@@ -723,7 +723,7 @@ namespace {
         PAIRCASE (SpaceKind::Constructor, SpaceKind::Constructor): {
           // Optimization: If the heads of the constructors don't match then
           // the two are disjoint and their difference is the first space.
-          if (this->Head.compare(other.Head) != 0) {
+          if (this->Head != other.Head) {
             return *this;
           }