Currently the build fails with 'arch/mips/vdso/vdso.so.dbg' already contains a '.MIPS.abiflags' section if the file already exists from a prior build. Add a makefile rule to force the rebuild of vdso.so.dbg if genvdso has has been changed to workaround the failure. Signed-off-by: Jo-Philipp Wich <jo@mein.io>