Gentoo's abseil-cpp-20260107.1 exports a C++20 usage requirement. MIGraphX
appends a raw C++17 compiler option, which overrides the standard selected
by CMake for targets consuming Abseil through protobuf and causes generated
protobuf sources to fail when they include Abseil headers.

Declare MIGraphX's C++17 baseline through CMake's standard properties. This
preserves C++17 for the rest of MIGraphX while allowing CMake to raise the
protobuf targets to the C++20 standard required by Abseil. The ONNX and
TensorFlow frontends already propagate protobuf's usage requirements
upstream. Accept the moved accumulator used by C++20's std::accumulate
implementation in the grid-sample parser.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -194,12 +194,9 @@
     add_compile_definitions("$<$<COMPILE_LANGUAGE:C,CXX>:_CRT_SECURE_NO_WARNINGS;_USE_MATH_DEFINES>")
 endif()

-set(CMAKE_CXX_STANDARD_DEFAULT "")
-if(MSVC)
-    add_compile_options($<$<COMPILE_LANGUAGE:CXX>:/std:c++17>)
-else()
-    add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-std=c++17>)
-endif()
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)

 include(EnableCompilerWarnings)
 include(ROCMClangTidy)
--- a/src/onnx/parse_gridsample.cpp
+++ b/src/onnx/parse_gridsample.cpp
@@ -173,7 +173,7 @@
         return std::accumulate(std::next(instructions.begin()),
                                instructions.end(),
                                instructions.front(),
-                               [&info](auto& ret, auto& ins) {
+                               [&info](auto ret, auto& ins) {
                                    return info.add_instruction(
                                        make_op("concat", {{"axis", 0}}), ret, ins);
                                });
@@ -186,7 +186,7 @@
         return std::accumulate(std::next(instructions.begin()),
                                instructions.end(),
                                instructions.front(),
-                               [&info, &dim](auto& ret, auto& ins) {
+                               [&info, &dim](auto ret, auto& ins) {
                                    return info.add_instruction(
                                        make_op("concat", {{"axis", dim}}), ret, ins);
                                });
@@ -535,7 +535,7 @@
         auto weights_t = std::accumulate(std::next(corner_weights.begin()),
                                          corner_weights.end(),
                                          corner_weights.front(),
-                                         [&info](auto& acc, auto& ins) {
+                                         [&info](auto acc, auto& ins) {
                                              return info.add_instruction(
                                                  make_op("concat", {{"axis", 1}}), acc, ins);
                                          });