[clang][ssaf] Fix plugin crash on AIX by adding SUPPORT_PLUGINS to clang-ssaf-format (#192292)

This change fixes a crash when running the `with-plugin.test` lit tests
on AIX. The crash is caused by a missing `-Wl, -brtl` linker flag.
Without this flag, the dynamic linker cannot resolve symbols from the
host executable when loading shared libraries via `dlopen`. So when the
plugin's static initializer runs and tries to register into the
`llvm::Registry` (calling `getRegistryLinkListInstance` defined in the
host via `LLVM_INSTANTIATE_REGISTRY`), the symbol resolves to `null`,
crashing the process.

The fix is to use `SUPPORT_PLUGINS` flag in `add_llvm_executable`, like
other tools in llvm. For AIX, this flag adds `-Wl, -brtl` to enable
runtime linking; for Non-AIX platforms, it sets `LLVM_NO_DEAD_STRIP` to
prevent the linker from stripping symbols that plugins reference at load
time.

clang/tools/clang-ssaf-format/CMakeLists.txt

@@ -3,8 +3,13 @@ set(LLVM_LINK_COMPONENTS
   Support
   )
 
+if(CLANG_PLUGIN_SUPPORT)
+  set(support_plugins SUPPORT_PLUGINS)
+endif()
+
 add_clang_tool(clang-ssaf-format
   SSAFFormat.cpp
+  ${support_plugins}
   )
 
 clang_target_link_libraries(clang-ssaf-format