The path associated with the -isysroot compiler flag can be supplied either as a separate argument or in the same argument as -isysroot itself. The places in library code that do special handling of this flag should support both forms, but currently only support the two separate arguments form. This means that the flag may not be removed when pointing to a nonexistent SDK or when a different SDK is specified in the user's CFLAGS, and at worst a ValueError is raised in compiler_fixup.