Mingw64: add a statically linked library adds libstdc++ dependency - static-libraries

Question

I want to accomplish a c++ executable that links to another c++ library of my own without a libstdc++ dependency. I can create such a c++ executable without the library without difficulty. But as soon as I link it to my library, the executable now has a libstdc++ dependency. A requirement is to NOT need to copy libstdc++6.dll (or any other .dll) onto Windows.
I'm building on Linux (Centos 7) using the latest mingw64 (x86_64-w64-mingw32-gcc (GCC) 4.9.3), cross compiling to Windows. Building on MSYS2/MingW has the same unwanted result.
(BTW, I have both libstdc++-static and glibc-static installed)
In the example, two lines are marked "COMMENT ME OUT": one in hello_c/main.cpp and the other in hello_c/CMakeLists.txt. If you comment these out, the reference to the hello_lib library is removed; the project builds and the executable executes on Windows 10 without a libstdc++ dependency. If you uncomment the two lines, the function in the hello_lib library is linked in; the project builds, but won't execute on Windows 10 due to the libstdc++ dependency. (Note: in powershell it silently fails, in an old-school dos/cmd box it displays an error message.)
The example has this structure:
hello_lib/library.cpp
hello_lib/library.h
hello_lib/CMakeLists.txt
hello_c/main.cpp
hello_c/CMakeLists.xt
buildme.sh
toolchain.cmake
## hello_lib/library.h:
int hello();
// hello_lib/library.cpp:
#include "library.h"
int hello() {
return 666;
}
## hello_lib CMakeLists.txt:
cmake_minimum_required(VERSION 3.13)
project(hello_lib)
set(CMAKE_CXX_STANDARD 11)
if(MINGW)
# Including these flags on Linux on Linux build = "Missing ELF Interpreter" error
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static -static-libgcc -static-libstdc++")
endif()
add_library(hello_lib STATIC library.cpp)
## hello_c/main.cpp:
#include <iostream>
#include "../hello_lib/library.h"
int main() {
std::cout << "Hello, world" << std::endl;
//COMMENT ME OUT:
printf("x = %d\n", hello());
return 0;
}
## hello_c CMakeLists.txt:
cmake_minimum_required(VERSION 3.13)
project(hello_c)
set(CMAKE_CXX_STANDARD 11)
if(MINGW)
# Including these flags on Linux on Linux build = "Missing ELF Interpreter" error
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static -static-libgcc -static-libstdc++")
endif()
link_directories(../hello_lib/cmake-build-debug)
add_executable(hello_c main.cpp)
# COMMENT ME OUT:
target_link_libraries(hello_c -static-libgcc -static-libstdc++ libhello_lib.a)
## buildme.sh:
#!/bin/bash
set -e
for i in hello_lib hello_c
do
rm -rf $i/cmake-build-debug
mkdir $i/cmake-build-debug
pushd $i/cmake-build-debug
# For building Win64 on Linux (with MinW64):
cmake .. -DCMAKE_TOOLCHAIN_FILE="../toolchain.cmake" -DCMAKE_BUILD_TYPE=Debug
# For building Win64 on Win64/MSYS2/MinW64:
#cmake .. -G "MSYS Makefiles" -DCMAKE_BUILD_TYPE=Debug
# For building Linux on Linux
#cmake .. -DCMAKE_BUILD_TYPE=Debug
make
popd
done
## toolchain.cmake:
set(CMAKE_SYSTEM_NAME Windows)
set(TOOLCHAIN_PREFIX x86_64-w64-mingw32)
set(CMAKE_C_COMPILER ${TOOLCHAIN_PREFIX}-gcc)
set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PREFIX}-g++)
set(CMAKE_RC_COMPILER ${TOOLCHAIN_PREFIX}-windres)
set(CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PREFIX})
With both MingW64 on Linux, and MingW64/MSYS2 on Windows 10, I get the libstdc++ dependency when I link with the 'hello_lib' library. In both cases if I comment out the reference to hello_lib, the libstdc++ dependency is eliminated.