How to stop MinGW and MSYS from mangling path names given at the command line

There is a way to suppress the path translation by setting MSYS_NO_PATHCONV=1 in Windows Git MSys or MSYS2_ARG_CONV_EXCL="*" in MSYS2.

Alternatively, you can set the variable only temporarily just for that command by putting the assignment just before the command itself:

MSYS_NO_PATHCONV=1 arm-none-linux-gnueabi-gcc.exe -Wall -g \
    -Wl,--dynamic-linker=/usr/lib/myrpath/ld-linux.so.3 \
    -Wl,-rpath=/usr/lib/myrpath \
    -I../targetsysroot/usr/include \
    myprogram.c -o myprogram

I just discovered a neat trick to avoid MSYS/MinGW translating the paths for you.

If you use double-slash to start the path, then MSYS won't translate the path to DOS format. So in OP's example, the -rpath switch should be specified like this:

-Wl,-rpath=//usr/lib/myrpath

All Unix/Linux tools seem to handle such spurious slashes without any problem, so even though your binary's rpath will start with //usr/... I think the loader will do the right thing.