[AIX] Enable rtl for plugins test

On AIX, the plugins are linked with `-WL,-G`, which produces shared objects enabled for use with the run-time linker. This patch sets the run-time
linker at the main executable link step to allow symbols from the plugins shared objects to be properly bound.

Reviewed By: daltenty

Differential Revision: https://reviews.llvm.org/D112275

Author: steven-wan-yu

llvm/unittests/Passes/CMakeLists.txt

@@ -12,6 +12,11 @@ endif()
 # work with DLLs on Windows (where a shared library can't have undefined
 # references), so just skip this testcase on Windows.
 if (NOT WIN32)
+  # On AIX, enable run-time linking to allow symbols from the plugins shared
+  # objects to be properly bound.
+  if(CMAKE_SYSTEM_NAME STREQUAL "AIX")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-brtl")
+  endif()
   set(LLVM_LINK_COMPONENTS Support Passes Core AsmParser)
   add_llvm_unittest(PluginsTests
     PluginsTest.cpp