JIT: Fix encoding cross-jumps at JIT time (dotnet#93851)

In 7db4f33 I made the assumption that cross-jumps only appear while
prejitting (and thus while recording relocations). However, the fake
splitting stress mode runs during JIT and thus will hit the assert. Make
the logic handle JIT time splitting as well.

Fix dotnet#93848

src/coreclr/jit/emitxarch.cpp

@@ -15844,25 +15844,38 @@ BYTE* emitter::emitOutputLJ(insGroup* ig, BYTE* dst, instrDesc* i)
         // For forward jumps, record the address of the distance value
         id->idjTemp.idjAddr = (dstOffs > srcOffs) ? dst : nullptr;
 
-        // Cross jumps may not be encodable in a 32-bit displacement as the
-        // hot/cold code buffers may be allocated arbitrarily far away from
-        // each other. We simply encode a 0 under the assumption that the
-        // relocations will take care of it.
         bool crossJump = emitJumpCrossHotColdBoundary(srcOffs, dstOffs);
-        assert(!crossJump || emitComp->opts.compReloc);
 
-        dst += emitOutputLong(dst, crossJump ? 0 : distVal);
+        int32_t encodedDisplacement;
+        if (emitComp->opts.compReloc && (!relAddr || crossJump))
+        {
+            // Cross jumps may not be encodable in a 32-bit displacement as the
+            // hot/cold code buffers may be allocated arbitrarily far away from
+            // each other. Similarly, absolute addresses when cross compiling
+            // for 32-bit may also not be representable. We simply encode a 0
+            // under the assumption that the relocations will take care of it.
+            encodedDisplacement = 0;
+        }
+        else
+        {
+            // For all other cases the displacement should be encodable in 32
+            // bits.
+            assert((distVal >= INT32_MIN) && (distVal <= INT32_MAX));
+            encodedDisplacement = static_cast<int32_t>(distVal);
+        }
+
+        dst += emitOutputLong(dst, encodedDisplacement);
 
         if (emitComp->opts.compReloc)
         {
             if (!relAddr)
             {
-                emitRecordRelocation((void*)(dst - sizeof(INT32)), (void*)distVal, IMAGE_REL_BASED_HIGHLOW);
+                emitRecordRelocation((void*)(dst - sizeof(int32_t)), (void*)distVal, IMAGE_REL_BASED_HIGHLOW);
             }
             else if (crossJump)
             {
                 assert(id->idjKeepLong);
-                emitRecordRelocation((void*)(dst - sizeof(INT32)), dst + distVal, IMAGE_REL_BASED_REL32);
+                emitRecordRelocation((void*)(dst - sizeof(int32_t)), dst + distVal, IMAGE_REL_BASED_REL32);
             }
         }
     }