[compiler][cleanup] Nicer printing of gap moves

Avoid the trailing ";" after the last parallel gap move. Instead, make the
semicolon part of the delimiter between moves.

Before:
gap ([stack:8|w32] = [constant:0];) ([edi|R|w32] = [constant:7]; [edx|R|w32] = [constant:8];)
After:
gap ([stack:8|w32] = [constant:0]) ([edi|R|w32] = [constant:7]; [edx|R|w32] = [constant:8])

R=mslekova@chromium.org

Bug: v8:12330
Change-Id: If9f3d67f09e48f717e839fa7fb8968f20bb58b16
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3347820Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78407}

src/compiler/backend/instruction.cc

@@ -284,7 +284,7 @@ std::ostream& operator<<(std::ostream& os, const MoveOperands& mo) {
   if (!mo.source().Equals(mo.destination())) {
     os << " = " << mo.source();
   }
-  return os << ";";
+  return os;
 }
 
 bool ParallelMove::IsRedundant() const {
@@ -373,11 +373,11 @@ bool Instruction::AreMovesRedundant() const {
 void Instruction::Print() const { StdoutStream{} << *this << std::endl; }
 
 std::ostream& operator<<(std::ostream& os, const ParallelMove& pm) {
-  const char* space = "";
+  const char* delimiter = "";
   for (MoveOperands* move : pm) {
     if (move->IsEliminated()) continue;
-    os << space << *move;
-    space = " ";
+    os << delimiter << *move;
+    delimiter = "; ";
   }
   return os;
 }