CMake Error:
ninja: error: build.ninja:1485: multiple rules generate ...
phonenumbers/metadata.h [-w dupbuild=err] 

Also Eliminate -Werror to fix sparc64 build

Index: cpp/CMakeLists.txt
--- cpp/CMakeLists.txt.orig
+++ cpp/CMakeLists.txt
@@ -18,7 +18,7 @@ cmake_minimum_required (VERSION 3.11)
 
 # Pick the C++ standard to compile with.
 # Abseil currently supports C++11, C++14, and C++17.
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 project (libphonenumber)
@@ -126,6 +126,8 @@ if (${USE_BOOST} STREQUAL "OFF" AND ${USE_STDMUTEX} ST
   find_package (Threads)
 endif()
 
+find_package (absl REQUIRED)
+
 find_or_build_gtest ()
 
 if (${USE_RE2} STREQUAL "ON")
@@ -356,7 +358,7 @@ add_metadata_gen_target (
   ${TEST_METADATA_TARGET}
   "${RESOURCES_DIR}/PhoneNumberMetadataForTesting.xml"
   "test_metadata"
-  "metadata"
+  "test_metadata"
 )
 list (APPEND TESTING_LIBRARY_SOURCES "src/phonenumbers/test_metadata.cc")
 
@@ -386,7 +388,7 @@ if (${USE_ICU_REGEXP} STREQUAL "ON")
 endif ()
 
 if (NOT WIN32)
-  add_definitions ("-Wall -Werror")
+  add_definitions ("-Wall")
 endif ()
 
 include_directories ("src")
