[ORC] Add default visibility to required JIT functions (#86322)

If you build LLVM with `-DCMAKE_CXX_VISIBILITY_PRESET=hidden` to help
reduce binary size, these symbols end up becoming local, and getting
stripped. This forces default visibility to override the global setting
in that case.

Relevant:
#62815 (comment)

Author: keith

llvm/lib/ExecutionEngine/Orc/TargetProcess/JITLoaderGDB.cpp

@@ -26,11 +26,13 @@ extern "C" {
 // We put information about the JITed function in this global, which the
 // debugger reads.  Make sure to specify the version statically, because the
 // debugger checks the version before we can set it during runtime.
+LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 struct jit_descriptor __jit_debug_descriptor = {JitDescriptorVersion, 0,
                                                 nullptr, nullptr};
 
 // Debuggers that implement the GDB JIT interface put a special breakpoint in
 // this function.
+LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 LLVM_ATTRIBUTE_NOINLINE void __jit_debug_register_code() {
   // The noinline and the asm prevent calls to this function from being
   // optimized out.