Fixed the build of Clang's unit tests on MinGW. Also removed some
unnecesary conditionals and introduced a new convenience function.

The problem was that the list of libraries for Clang's unit tests was
<clang libraries> <system libraries> <llvm libraries>. As the llvm
libraries references symbols defined on the system libraries, those
were reported as undefined.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128484 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/cmake/modules/AddLLVM.cmake b/cmake/modules/AddLLVM.cmake
index f0dc106..df739b4 100755
--- a/cmake/modules/AddLLVM.cmake
+++ b/cmake/modules/AddLLVM.cmake
@@ -11,10 +11,12 @@
 
   if( BUILD_SHARED_LIBS )
     llvm_config( ${name} ${LLVM_LINK_COMPONENTS} )
-    get_system_libs(sl)
-    target_link_libraries( ${name} ${sl} )
   endif()
 
+  # Ensure that the system libraries always comes last on the
+  # list. Without this, linking the unit tests on MinGW fails.
+  link_system_libs( ${name} )
+
   install(TARGETS ${name}
     LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
     ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX})
@@ -47,8 +49,7 @@
     set_target_properties( ${name} PROPERTIES PREFIX "" )
 
     llvm_config( ${name} ${LLVM_LINK_COMPONENTS} )
-    get_system_libs(sl)
-    target_link_libraries( ${name} ${sl} )
+    link_system_libs( ${name} )
 
     if (APPLE)
       # Darwin-specific linker flags for loadable modules.
@@ -73,21 +74,12 @@
     add_executable(${name} ${ALL_FILES})
   endif()
   set(EXCLUDE_FROM_ALL OFF)
-  if( LLVM_USED_LIBS )
-    foreach(lib ${LLVM_USED_LIBS})
-      target_link_libraries( ${name} ${lib} )
-    endforeach(lib)
-  endif( LLVM_USED_LIBS )
-  if( LLVM_LINK_COMPONENTS )
-    llvm_config(${name} ${LLVM_LINK_COMPONENTS})
-  endif( LLVM_LINK_COMPONENTS )
+  target_link_libraries( ${name} ${LLVM_USED_LIBS} )
+  llvm_config( ${name} ${LLVM_LINK_COMPONENTS} )
   if( LLVM_COMMON_DEPENDS )
     add_dependencies( ${name} ${LLVM_COMMON_DEPENDS} )
   endif( LLVM_COMMON_DEPENDS )
-  get_system_libs(llvm_system_libs)
-  if( llvm_system_libs )
-    target_link_libraries(${name} ${llvm_system_libs})
-  endif()
+  link_system_libs( ${name} )
 endmacro(add_llvm_executable name)
 
 
diff --git a/cmake/modules/LLVMConfig.cmake b/cmake/modules/LLVMConfig.cmake
index fd1cfa8..bd6a7a2 100755
--- a/cmake/modules/LLVMConfig.cmake
+++ b/cmake/modules/LLVMConfig.cmake
@@ -16,6 +16,12 @@
 endfunction(get_system_libs)
 
 
+function(link_system_libs target)
+  get_system_libs(llvm_system_libs)
+  target_link_libraries(${target} ${llvm_system_libs})
+endfunction(link_system_libs)
+
+
 function(is_llvm_target_library library return_var)
   # Sets variable `return_var' to ON if `library' corresponds to a
   # LLVM supported target. To OFF if it doesn't.