Add N_NO_DEAD_STRIP flag to section symbols to ensure that data at th…

…e beginning of the section are not stripped if there's no other N_NO_DEAD_STRIP symbol referencing them (#106444)

Extracted from #106224.

PR #103039 added `N_NO_DEAD_STRIP` flag to all symbols emitted by ILC and enabled the dead code stripping in the native linker.

It failed to handle one specific edge case that is luckily not happening in the wild. If the first node emitted into a section has a symbol with non-zero offset NN the first `N_NO_DEAD_STRIP` symbol is not pointing at the start of the section. The native linker then splits up the section into atom and the first atom from offset 0 to offset NN is never referenced and becomes eligible for dead code stripping. Since we emit a symbol for each section start (for use in section-relative relocations) we can just mark the symbol with `N_NO_DEAD_STRIP` to resolve the issue.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/ObjectWriter/MachObjectWriter.cs

@@ -113,7 +113,7 @@ private protected override void EmitSectionsAndLayout()
                     Name = $"lsection{sectionIndex}",
                     Section = section,
                     Value = section.VirtualAddress,
-                    Descriptor = 0,
+                    Descriptor = N_NO_DEAD_STRIP,
                     Type = N_SECT,
                 };
                 _symbolTable.Add(machSymbol);