build: Require and build with C++ 17

configure.ac

@@ -61,8 +61,8 @@ case $host in
      lt_cv_deplibs_check_method="pass_all"
   ;;
 esac
-dnl Require C++11 compiler (no GNU extensions)
-AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory])
+dnl Require C++17 compiler (no GNU extensions)
+AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 dnl Check if -latomic is required for <std::atomic>
 CHECK_ATOMIC
 

src/leveldb/build_detect_platform

@@ -56,7 +56,7 @@ fi
 COMMON_FLAGS=
 CROSS_COMPILE=
 PLATFORM_CCFLAGS=
-PLATFORM_CXXFLAGS=
+PLATFORM_CXXFLAGS="-std=c++17"
 PLATFORM_LDFLAGS=
 PLATFORM_LIBS=
 PLATFORM_SHARED_EXT="so"
@@ -203,18 +203,9 @@ if [ "$CROSS_COMPILE" = "true" ]; then
 else
     CXXOUTPUT="${TMPDIR}/leveldb_build_detect_platform-cxx.$$"
 
-    # If -std=c++0x works, use <atomic> as fallback for when memory barriers
+    # As -std=c++17 works, use <atomic> as fallback for when memory barriers
     # are not available.
-    $CXX $CXXFLAGS -std=c++0x -x c++ - -o $CXXOUTPUT 2>/dev/null  <<EOF
-      #include <atomic>
-      int main() {}
-EOF
-    if [ "$?" = 0 ]; then
-        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX -DLEVELDB_ATOMIC_PRESENT"
-        PLATFORM_CXXFLAGS="-std=c++0x"
-    else
-        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX"
-    fi
+    COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX -DLEVELDB_ATOMIC_PRESENT"
 
     # Test whether tcmalloc is available
     $CXX $CXXFLAGS -x c++ - -o $CXXOUTPUT -ltcmalloc 2>/dev/null  <<EOF