domsuspend: Fix warning on mingw build

domsuspend: Fix warning on mingw build

Commit d82170d introduced a workaround for domtop: in that example
program, we define a symbol called ERROR for our own use, but since
a symbol with the same name is already defined in one of mingw's
header files, we get a warning when using that compiler.

domsuspend defines the same problematic symbol, so the workaround
has been copied over.