[JITLink][aarch64] Pointer jump stubs should have 4-byte alignment.

Pointer jump stubs content was incorrectly using 1-byte alignment. This bug
flew under the radar because the ordinary instruction streams (and aligned
section starts) usually left the block 4-byte aligned anyway. The bug was
observed when an out-of-tree pass introduced new content with arbitrary sizes
into the text section.

No testcase yet: We don't have a good way to replicate the perturbation that
was caused by the out-of-tree pass.

llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h

@@ -646,7 +646,7 @@ inline Symbol &createAnonymousPointer(LinkGraph &G, Section &PointerSection,
 inline Block &createPointerJumpStubBlock(LinkGraph &G, Section &StubSection,
                                          Symbol &PointerSymbol) {
   auto &B = G.createContentBlock(StubSection, PointerJumpStubContent,
-                                 orc::ExecutorAddr(~uint64_t(11)), 1, 0);
+                                 orc::ExecutorAddr(~uint64_t(11)), 4, 0);
   B.addEdge(Page21, 0, PointerSymbol, 0);
   B.addEdge(PageOffset12, 4, PointerSymbol, 0);
   return B;