[Offload] Remove support for old "BUILD_PLUGIN" options. (#91644)

Summary:
Since the move to the statically linked plugins, we added a new way to
directly control which plugins will be added. Delete these old ones as
they will cause the build to fail and suggest the new format.

Author: jhuber6

offload/CMakeLists.txt

@@ -151,13 +151,19 @@ if (NOT LIBOMPTARGET_LLVM_INCLUDE_DIRS)
   message(FATAL_ERROR "Missing definition for LIBOMPTARGET_LLVM_INCLUDE_DIRS")
 endif()
 
+if(DEFINED LIBOMPTARGET_BUILD_CUDA_PLUGIN OR 
+   DEFINED LIBOMPTARGET_BUILD_AMDGPU_PLUGIN)
+  message(WARNING "Option removed, use 'LIBOMPTARGET_PLUGINS_TO_BUILD' instead")
+endif()
+
 set(LIBOMPTARGET_ALL_PLUGIN_TARGETS amdgpu cuda host)
 set(LIBOMPTARGET_PLUGINS_TO_BUILD "all" CACHE STRING
     "Semicolon-separated list of plugins to use: cuda, amdgpu, host or \"all\".")
 
 if(LIBOMPTARGET_PLUGINS_TO_BUILD STREQUAL "all")
   set(LIBOMPTARGET_PLUGINS_TO_BUILD ${LIBOMPTARGET_ALL_PLUGIN_TARGETS})
 endif()
+message("Building with support for ${LIBOMPTARGET_PLUGINS_TO_BUILD} plugins")
 
 set(LIBOMPTARGET_ENUM_PLUGIN_TARGETS "")
 foreach(plugin IN LISTS LIBOMPTARGET_PLUGINS_TO_BUILD)

offload/plugins-nextgen/amdgpu/CMakeLists.txt

@@ -12,13 +12,6 @@
 ##===----------------------------------------------------------------------===##
 
 ################################################################################
-set(LIBOMPTARGET_BUILD_AMDGPU_PLUGIN TRUE CACHE BOOL
-  "Whether to build AMDGPU plugin")
-if (NOT LIBOMPTARGET_BUILD_AMDGPU_PLUGIN)
-  libomptarget_say("Not building AMDGPU NextGen offloading plugin: LIBOMPTARGET_BUILD_AMDGPU_PLUGIN is false")
-  return()
-endif()
-
 # as of rocm-3.7, hsa is installed with cmake packages and kmt is found via hsa
 find_package(hsa-runtime64 QUIET 1.2.0 HINTS ${CMAKE_INSTALL_PREFIX} PATHS /opt/rocm)
 

offload/plugins-nextgen/cuda/CMakeLists.txt

@@ -9,13 +9,6 @@
 # Build a plugin for a CUDA machine if available.
 #
 ##===----------------------------------------------------------------------===##
-set(LIBOMPTARGET_BUILD_CUDA_PLUGIN TRUE CACHE BOOL
-  "Whether to build CUDA plugin")
-if (NOT LIBOMPTARGET_BUILD_CUDA_PLUGIN)
-  libomptarget_say("Not building CUDA NextGen offloading plugin: LIBOMPTARGET_BUILD_CUDA_PLUGIN is false")
-  return()
-endif()
-
 if (NOT (CMAKE_SYSTEM_PROCESSOR MATCHES "(x86_64)|(ppc64le)|(aarch64)$" AND CMAKE_SYSTEM_NAME MATCHES "Linux"))
   libomptarget_say("Not building CUDA NextGen offloading plugin: only support CUDA in Linux x86_64, ppc64le, or aarch64 hosts.")
   return()