passing extra arguments to devtools::build

This question was posed on SO : 
https://stackoverflow.com/questions/58118495/passing-extra-argumenets-to-devtoolsbuild 
but there has been no useful reply.

Something seems to have changed in the |devtools|package, so that the 
following commands, that used to run now give an error I can't decipher:

|>Sys.setenv(R_GSCMD="C:/Program 
Files/gs/gs9.21/bin/gswin64c.exe")>devtools::build(args 
=c('--resave-data','--compact-vignettes="gs+qpdf"'))The 
filename,directory name,or volume label syntax is incorrect. Error 
in(function(command =NULL,args =character(),error_on_status 
=TRUE,:System command error|

I've tried other alternatives with other |devtools| commands, like just 
passing a single argument, but still get the same error

|args ='--compact-vignettes="gs+qpdf"'devtools::check_win_devel(args=args)|

I'm using devtools 2.2.0, under R 3.5.2