[Libomptarget] Rework interface for enabling plugins (#86875)

Summary:
Previously we would build all of the plugins by default and then only
load some using the `LIBOMPTARGET_PLUGINS_TO_LOAD` variable. This patch
renamed this to `LIBOMPTARGET_PLUGINS_TO_BUILD` and changes whether or
not it will include the plugin in CMake.

Additionally this patch creates a new `Targets.def` file that allows us
to enumerate all of the enabled plugins. This is somewhat different from
the old method, and it's done this way for future use that will need to
be shared. This follows the same method that LLVM uses for its targets,
however it does require adding an extra include path.

Depends on https://github.com/llvm/llvm-project/pull/86868

1 files changed, 20 insertions, 0 deletions

diff --git a/offload/include/Shared/Targets.def.in b/offload/include/Shared/Targets.def.in
new file mode 100644
index 000000000000..f34b523b4542
--- /dev/null
+++ b/offload/include/Shared/Targets.def.in
@@ -0,0 +1,20 @@
+//===-- Shared/Targets.def - Target plugin enumerator -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Enumerates over all of the supported target plugins that are available to
+// the offloading library.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef PLUGIN_TARGET
+#  error Please define the macro PLUGIN_TARGET(TargetName)
+#endif
+
+@LIBOMPTARGET_ENUM_PLUGIN_TARGETS@
+
+#undef PLUGIN_TARGET