Revert "[Orc][LLJIT] Use JITLink even if a custom JITTargetMachineBuilder is supplied."

This reverts commit 298e183e813c884dd22816383405bae3ef9ef278.

This commit caused some build failures -- reverting while I investigate.
diff --git a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
index 54473ab..5c39373 100644
--- a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
@@ -24,15 +24,11 @@
       JTMB = std::move(*JTMBOrErr);
     else
       return JTMBOrErr.takeError();
-  }
 
-  // If the client didn't configure any linker options then auto-configure the
-  // JIT linker.
-  if (!CreateObjectLinkingLayer && JTMB->getCodeModel() == None &&
-      JTMB->getRelocationModel() == None) {
-
+    // If no ObjectLinkingLayer creator was set and the target supports JITLink
+    // then configure for JITLink.
     auto &TT = JTMB->getTargetTriple();
-    if (TT.isOSBinFormatMachO() &&
+    if (!CreateObjectLinkingLayer && TT.isOSBinFormatMachO() &&
         (TT.getArch() == Triple::aarch64 || TT.getArch() == Triple::x86_64)) {
 
       JTMB->setRelocationModel(Reloc::PIC_);