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. Propagate
protobuf's usage requirements to the ONNX and TensorFlow frontends, whose
sources include the generated protobuf headers. Accept the moved accumulator
used by C++20's std::accumulate implementation in the grid-sample parser.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -142,9 +142,6 @@
 
-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)

--- a/src/onnx/CMakeLists.txt
+++ b/src/onnx/CMakeLists.txt
@@ -28,7 +28,7 @@
     protobuf_generate(TARGET onnx-proto PROTOS onnx.proto)
     target_include_directories(onnx-proto SYSTEM PUBLIC ${CMAKE_CURRENT_BINARY_DIR} ${PROTOBUF_INCLUDE_DIR})
     target_link_libraries(onnx-proto PRIVATE ${PROTOBUF_LIBRARY})
-    target_link_libraries(onnx-proto PRIVATE protobuf::libprotobuf)
+    target_link_libraries(onnx-proto PUBLIC protobuf::libprotobuf)
 else()
     find_package(Protobuf REQUIRED)
     protobuf_generate_cpp(PROTO_SRCS PROTO_HDRS onnx.proto)
--- a/src/tf/CMakeLists.txt
+++ b/src/tf/CMakeLists.txt
@@ -41,7 +41,7 @@
     )
     target_include_directories(tf-proto SYSTEM PUBLIC ${CMAKE_CURRENT_BINARY_DIR} ${PROTOBUF_INCLUDE_DIR})
     target_link_libraries(tf-proto PRIVATE ${PROTOBUF_LIBRARY})
-    target_link_libraries(tf-proto PRIVATE protobuf::libprotobuf)
+    target_link_libraries(tf-proto PUBLIC protobuf::libprotobuf)
 else()
     find_package(Protobuf REQUIRED)
     protobuf_generate_cpp(
--- a/src/onnx/parse_gridsample.cpp
+++ b/src/onnx/parse_gridsample.cpp
@@ -168,7 +168,7 @@ struct grid_sampler
         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);
                                });
@@ -181,7 +181,7 @@ struct grid_sampler
         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);
                                });
@@ -530,7 +530,7 @@ struct cubic_sampler : grid_sampler
         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);
                                          });