Reland "[benchmarks] Move libcxx's fork of google/benchmark and llvm/utils'""

This reverts commit e7568b6 and relands
c6f7b72.

The culprit was: missed that libc also had a dependency on one of the
copies of `google-benchmark`

Also opportunistically fixed indentation from prev. change.

Differential Revision: https://reviews.llvm.org/D112012

Author: mtrofin

libc/benchmarks/CMakeLists.txt

@@ -17,7 +17,7 @@ string(REPLACE ";" " " GOOGLE_BENCHMARK_TARGET_FLAGS "${GOOGLE_BENCHMARK_TARGET_
 ExternalProject_Add(google-benchmark
     EXCLUDE_FROM_ALL ON
     PREFIX google-benchmark
-    SOURCE_DIR ${LIBC_SOURCE_DIR}/../llvm/utils/benchmark
+    SOURCE_DIR ${LLVM_THIRD_PARTY_DIR}/benchmark
     INSTALL_DIR ${CMAKE_CURRENT_BINARY_DIR}/google-benchmark
     CMAKE_CACHE_ARGS
         -DBUILD_SHARED_LIBS:BOOL=OFF

libcxx/benchmarks/CMakeLists.txt

@@ -41,7 +41,7 @@ ExternalProject_Add(google-benchmark-libcxx
         EXCLUDE_FROM_ALL ON
         DEPENDS cxx cxx-headers
         PREFIX benchmark-libcxx
-        SOURCE_DIR ${LIBCXX_SOURCE_DIR}/utils/google-benchmark
+	      SOURCE_DIR ${LLVM_THIRD_PARTY_DIR}/benchmark
         INSTALL_DIR ${CMAKE_CURRENT_BINARY_DIR}/benchmark-libcxx
         CMAKE_CACHE_ARGS
           -DCMAKE_C_COMPILER:STRING=${CMAKE_C_COMPILER}
@@ -66,7 +66,7 @@ if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
   ExternalProject_Add(google-benchmark-native
         EXCLUDE_FROM_ALL ON
         PREFIX benchmark-native
-        SOURCE_DIR ${LIBCXX_SOURCE_DIR}/utils/google-benchmark
+	      SOURCE_DIR ${LLVM_THIRD_PARTY_DIR}/benchmark
         INSTALL_DIR ${CMAKE_CURRENT_BINARY_DIR}/benchmark-native
         CMAKE_CACHE_ARGS
           -DCMAKE_C_COMPILER:STRING=${CMAKE_C_COMPILER}