How to statically link missing libgcc_s_seh-1.dll and libstdc++-6.dll DLLs for 9.3-win32 MinGW executable

I want to compile a simple Windows application on Linux using MinGW. I compile as follows: x86_64-w64-mingw32-g++ -L. -l:mathlib.dll -o fib main.cpp mathlib.h This results in an executable fib that computes the N'th fibonacci number using a function imported from mathlib.dll. Now, when executing fib on Windows, it complains that libgcc_s_seh-1.dll and libstdc++-6.dll are missing. If I copy these DLLs to Windows, then everything works, but I'd like not to copy these MinGW dependencies with every executable. How can I statically link these MinGW depencies, such that foo depends on no other DLLs than mathlib.dll?