Allow for custom code model in clang::Interpreter (llvm#156977)

This is necessary when using ASan, since the larger code size will lead
to errors such as:

```
JIT session error: In graph clojure_core-clojure.core$clojure_core_cpp_cast_24538-24543-jitted-objectbuffer, section .eh_frame: relocation target 0x7bffe374b000 (DW.ref.__gxx_personality_v0) is out of range of Delta32 fixup at address 0x7bffe374b000 (<anonymous block> @ 0x7fffebf48158 + 0x13)
```

Previously, `clang::Interpreter` would hard-code the usage of a small
code model. With this change, we default to small, but allow for custom
values. This related to llvm#102858 and llvm#135401.

There is no change to default behavior here.

@lhames for review.

Author: jeaye

clang/include/clang/Interpreter/Interpreter.h

@@ -135,11 +135,13 @@ class Interpreter {
     std::string OrcRuntimePath = "";
     /// PID of the out-of-process JIT executor.
     uint32_t ExecutorPID = 0;
+    /// An optional code model to provide to the JITTargetMachineBuilder
+    std::optional<llvm::CodeModel::Model> CM = std::nullopt;
 
     JITConfig()
         : IsOutOfProcess(false), OOPExecutor(""), OOPExecutorConnect(""),
           UseSharedMemory(false), SlabAllocateSize(0), OrcRuntimePath(""),
-          ExecutorPID(0) {}
+          ExecutorPID(0), CM(std::nullopt) {}
   };
 
 protected:

clang/lib/Interpreter/Interpreter.cpp

@@ -647,6 +647,8 @@ llvm::Error Interpreter::CreateExecutor(JITConfig Config) {
     auto JTMB = createJITTargetMachineBuilder(TT);
     if (!JTMB)
       return JTMB.takeError();
+    if (Config.CM)
+      JTMB->setCodeModel(Config.CM);
     auto JB = IncrementalExecutor::createDefaultJITBuilder(std::move(*JTMB));
     if (!JB)
       return JB.takeError();