Fix integration of pass plugins with llvm dylib

Call llvm_process_pass_plugin from clang when in standalone mode.

Differential Revision: https://reviews.llvm.org/D74464

(cherry picked from commit d21664c)

Author: serge-sans-paille

clang/CMakeLists.txt

@@ -864,6 +864,7 @@ add_subdirectory(utils/hmaptool)
 
 if(CLANG_BUILT_STANDALONE)
   llvm_distribution_add_targets()
+  process_llvm_pass_plugins()
 endif()
 
 configure_file(

llvm/CMakeLists.txt

@@ -1069,6 +1069,7 @@ endif()
 # after all targets are created.
 include(LLVMDistributionSupport)
 llvm_distribution_add_targets()
+process_llvm_pass_plugins()
 
 # This allows us to deploy the Universal CRT DLLs by passing -DCMAKE_INSTALL_UCRT_LIBRARIES=ON to CMake
 if (MSVC AND CMAKE_HOST_SYSTEM_NAME STREQUAL "Windows" AND CMAKE_INSTALL_UCRT_LIBRARIES)
@@ -1093,5 +1094,3 @@ endif()
 if (LLVM_INCLUDE_UTILS AND LLVM_INCLUDE_TOOLS)
   add_subdirectory(utils/llvm-locstats)
 endif()
-
-process_llvm_pass_plugins()