[Build] Update C++ standard to C++17 for AOT, iOS, VTA

Follow-up from apache#12337 and
apache#12693, a few additional locations
that specify C++14.

Author: Lunderberg

apps/ios_rpc/tvmrpc.xcodeproj/project.pbxproj

@@ -255,7 +255,7 @@
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_ANALYZER_NONNULL = YES;
 				CLANG_ANALYZER_NUMBER_OBJECT_CONVERSION = YES_AGGRESSIVE;
-				CLANG_CXX_LANGUAGE_STANDARD = "gnu++14";
+				CLANG_CXX_LANGUAGE_STANDARD = "gnu++17";
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
@@ -308,7 +308,7 @@
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_ANALYZER_NONNULL = YES;
 				CLANG_ANALYZER_NUMBER_OBJECT_CONVERSION = YES_AGGRESSIVE;
-				CLANG_CXX_LANGUAGE_STANDARD = "gnu++14";
+				CLANG_CXX_LANGUAGE_STANDARD = "gnu++17";
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;

include/tvm/support/span.h

@@ -36,7 +36,7 @@ namespace support {
 /*!
  * \brief A partial implementation of the C++20 std::span.
  *
- * At the time of writing, TVM must compile against C++14.
+ * At the time of writing, TVM must compile against C++17.
  */
 template <class T, class W>
 class Span {

tests/python/relay/aot/test_cpp_aot.py

@@ -138,7 +138,7 @@ def test_mobilenet(enable_usmp, target_kind):
 
     temp_dir = tvm.contrib.utils.TempDirectory()
     test_so_path = temp_dir / "test.so"
-    mod.export_library(test_so_path, cc="c++", options=["-std=gnu++14", "-g3", "-O0"])
+    mod.export_library(test_so_path, cc="c++", options=["-std=gnu++17", "-g3", "-O0"])
     loaded_mod = tvm.runtime.load_module(test_so_path)
     runner = tvm.runtime.executor.AotModule(loaded_mod["default"](tvm.cpu(0)))
     runner.set_input(**inputs)

vta/python/vta/exec/rpc_server.py

@@ -106,7 +106,7 @@ def reconfig_runtime(cfg_json):
             if pkg.same_config(old_cfg):
                 logging.info("Skip reconfig_runtime due to same config.")
                 return
-        cflags = ["-O2", "-std=c++14"]
+        cflags = ["-O2", "-std=c++17"]
         cflags += pkg.cflags
         ldflags = pkg.ldflags
         lib_name = dll_path