Revert "[MC] Speed up AttemptToFoldSymbolOffsetDifference in the absence of MCAsmLayout"

Summary:
This reverts commit 92d2c1b67835248d5d7371fa06381f970687c68f.

Causes timeouts in BOLT tests

Test Plan: sandcastle

Reviewers: ayermolo, davidino, #llvm-bolt

Reviewed By: davidino

Differential Revision: https://phabricator.intern.facebook.com/D58066252

Tasks: T191101004

Tags: accept2ship, publish_when_ready

Author: aaupov

llvm/lib/MC/MCExpr.cpp

@@ -675,14 +675,8 @@ static void AttemptToFoldSymbolOffsetDifference(
     if (FA == FB) {
       Reverse = SA.getOffset() < SB.getOffset();
     } else if (!isa<MCDummyFragment>(FA)) {
-      // Testing FA < FB is slow. Use setLayoutOrder to speed up computation.
-      // The formal layout order will be finalized in MCAssembler::layout.
-      if (FA->getLayoutOrder() == 0 || FB->getLayoutOrder()== 0) {
-        unsigned LayoutOrder = 0;
-        for (MCFragment &F : *FA->getParent())
-          F.setLayoutOrder(++LayoutOrder);
-      }
-      Reverse = FA->getLayoutOrder() < FB->getLayoutOrder();
+      Reverse = std::find_if(std::next(FA->getIterator()), SecA.end(),
+                             [&](auto &I) { return &I == FB; }) != SecA.end();
     }
 
     uint64_t SAOffset = SA.getOffset(), SBOffset = SB.getOffset();