Revert "Move googletest to the third-party directory"

This reverts commit 59052468c3e38cab15582cefbb5133fd4c2ffce5.

It looks like this patch breaks the build when compiler-rt is passed to
LLVM_ENABLE_PROJECTS instead of LLVM_ENABLE_RUNTIMES.

GitOrigin-RevId: 8a084f68c8a1cac99d9fa0fbcf490b53ab3b6e0c
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e244a54..674c7e7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -639,7 +639,7 @@
 endif()
 
 # Unittests support.
-set(COMPILER_RT_GTEST_PATH ${LLVM_THIRD_PARTY_DIR}/unittest/googletest)
+set(COMPILER_RT_GTEST_PATH ${LLVM_MAIN_SRC_DIR}/utils/unittest/googletest)
 set(COMPILER_RT_GTEST_SOURCE ${COMPILER_RT_GTEST_PATH}/src/gtest-all.cc)
 set(COMPILER_RT_GTEST_CFLAGS
   -DGTEST_NO_LLVM_SUPPORT=1
@@ -649,7 +649,7 @@
 )
 
 # Mocking support.
-set(COMPILER_RT_GMOCK_PATH ${LLVM_THIRD_PATY_DIR}/unittest/googlemock)
+set(COMPILER_RT_GMOCK_PATH ${LLVM_MAIN_SRC_DIR}/utils/unittest/googlemock)
 set(COMPILER_RT_GMOCK_SOURCE ${COMPILER_RT_GMOCK_PATH}/src/gmock-all.cc)
 set(COMPILER_RT_GMOCK_CFLAGS
   -DGTEST_NO_LLVM_SUPPORT=1