Fix setting options in BuildAsync.

`makeprg` and `errorformat` is the global-local option.

`:help global-local`
> For example, you have two windows, both on C source code.  They use the global
> 'makeprg' option.  If you do this in one of the two windows:
> ```vim
> :set makeprg=gmake
> ```
> then the other window will switch to the same value.  There is no need to set
> the 'makeprg' option in the other C source window too.
> However, if you start editing a Perl file in a new window, you want to use
> another 'makeprg' for it, without changing the value used for the C source
> files.  You use this command:
> ```vim
> :setlocal makeprg=perlmake
> ```