[Offload] Properly report errors when jit compiling (llvm#145498)

Previously, if a binary failed to load due to failures when jit
compiling, the function would return success with nullptr. Now it
returns a new plugin error, `COMPILE_FAILURE`.

Author: RossBrunton

offload/liboffload/API/Common.td

@@ -104,6 +104,7 @@ def ErrorCode : Enum {
     Etor<"UNIMPLEMENTED", "generic error code for features currently unimplemented by the device/backend">,
     Etor<"UNSUPPORTED", "generic error code for features unsupported by the device/backend">,
     Etor<"ASSEMBLE_FAILURE", "assembler failure while processing binary image">,
+    Etor<"COMPILE_FAILURE", "jit compile failure while processing binary image">,
     Etor<"LINK_FAILURE", "linker failure while processing binary image">,
     Etor<"BACKEND_FAILURE", "the plugin backend is in an invalid or unsupported state">,
     Etor<"UNINITIALIZED", "not initialized">,

offload/liboffload/src/OffloadImpl.cpp

@@ -471,6 +471,7 @@ Error olCreateProgram_impl(ol_device_handle_t Device, const void *ProgData,
     delete Prog;
     return Res.takeError();
   }
+  assert(*Res != nullptr && "loadBinary returned nullptr");
 
   Prog->Image = *Res;
   *Program = Prog;

offload/plugins-nextgen/common/src/PluginInterface.cpp

@@ -909,8 +909,9 @@ GenericDeviceTy::loadBinary(GenericPluginTy &Plugin,
   if (!PostJITImageOrErr) {
     auto Err = PostJITImageOrErr.takeError();
     REPORT("Failure to jit IR image %p on device %d: %s\n", InputTgtImage,
-           DeviceId, toString(std::move(Err)).data());
-    return nullptr;
+           DeviceId, toStringWithoutConsuming(Err).data());
+    return Plugin::error(ErrorCode::COMPILE_FAILURE, std::move(Err),
+                         "failure to jit IR image");
   }
 
   // Load the binary and allocate the image object. Use the next available id