[AIX]Update CMake linker flags to allow clang/llvm debug build.

[azhan92]

Update buildllvm.sh file so default ld path doesn't override other linker flags.

llvm/cmake/modules/HandleLLVMOptions.cmake

if(${AR_RESULT} EQUAL 0)
     file(REMOVE ${CMAKE_BINARY_DIR}/t.a)
   endif()
 endif()
 
 if(${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   # -fPIC does not enable the large code model for GCC on AIX but does for XL.
   if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
     append("-mcmodel=large" CMAKE_CXX_FLAGS CMAKE_C_FLAGS)
+    append("-Wl, bglink=large"
+        CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   elseif(CMAKE_CXX_COMPILER_ID MATCHES "XL")
     # XL generates a small number of relocations not of the large model, -bbigtoc is needed.
     append("-Wl,-bbigtoc"
            CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
     # The default behaviour on AIX processes dynamic initialization of non-local variables with
     # static storage duration even for archive members that are otherwise unreferenced.
     # Since `--whole-archive` is not used by the LLVM build to keep such initializations for Linux,
     # we can limit the processing for archive members to only those that are otherwise referenced.