CMake: Consolidate gtest detection code

[tstellar]

Summary

This makes it possible to build the unittests with only the gtest sources
and without a full LLVM source tree.

[chandlerc]

I mean, sure.

I really don't know that supporting this ever expanding diversity of build strategies is worth its cost, but I don't see a specific reason to not take this patch....

[tstellar]

In D51567#1222704, @chandlerc wrote:

I mean, sure.

I really don't know that supporting this ever expanding diversity of build strategies is worth its cost, but I don't see a specific reason to not take this patch....

I actually agree with you that we don't want to be supporting every possible strategy in trunk. I usually try to keep Fedora specific stuff like this out of trunk, but in this case it looked like a useful code simplification that might be generally helpful.

[tstellar]

Dropping this since it is more Fedora specific.

CMakeLists.txt

if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)
       endif()
       if(NOT LLVM_UTILS_PROVIDED)
         add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/FileCheck utils/FileCheck)
         add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/count utils/count)
         add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/not utils/not)
         set(LLVM_UTILS_PROVIDED ON)
         set(CLANG_TEST_DEPS FileCheck count not)
       endif()
-      set(UNITTEST_DIR ${LLVM_MAIN_SRC_DIR}/utils/unittest)
-      if(EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h
-          AND NOT EXISTS ${LLVM_LIBRARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gtest${CMAKE_STATIC_LIBRARY_SUFFIX}
-          AND EXISTS ${UNITTEST_DIR}/CMakeLists.txt)
-        add_subdirectory(${UNITTEST_DIR} utils/unittest)
-      endif()
     else()
       # Seek installed Lit.
       find_program(LLVM_LIT
                    NAMES llvm-lit lit.py lit
                    PATHS "${LLVM_MAIN_SRC_DIR}/utils/lit"
                    DOC "Path to lit.py")
     endif()
 
if(NOT EXISTS ${CLANG_ORDER_FILE})
     else()
       message(FATAL_ERROR "Specified order file '${CLANG_ORDER_FILE}' does not exist.")
     endif()
   endif()
 endif()
 
 
 if( CLANG_INCLUDE_TESTS )
-  if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/unittest/googletest/include/gtest/gtest.h)
+  set(UNITTEST_DIR ${LLVM_MAIN_SRC_DIR}/utils/unittest)
+  if(EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
     add_subdirectory(unittests)
     list(APPEND CLANG_TEST_DEPS ClangUnitTests)
     list(APPEND CLANG_TEST_PARAMS
       clang_unit_site_config=${CMAKE_CURRENT_BINARY_DIR}/test/Unit/lit.site.cfg
       )
+    if (CLANG_BUILT_STANDALONE
+        AND NOT EXISTS ${LLVM_LIBRARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gtest${CMAKE_STATIC_LIBRARY_SUFFIX}
+        AND EXISTS ${UNITTEST_DIR}/CMakeLists.txt)
+      add_subdirectory(${UNITTEST_DIR} utils/unittest)
+    endif()
   endif()
   add_subdirectory(test)
 
   if(CLANG_BUILT_STANDALONE)
     # Add a global check rule now that all subdirectories have been traversed
     # and we know the total set of lit testsuites.
     get_property(LLVM_LIT_TESTSUITES GLOBAL PROPERTY LLVM_LIT_TESTSUITES)
     get_property(LLVM_LIT_PARAMS GLOBAL PROPERTY LLVM_LIT_PARAMS)