fix build on no-fork-spawnv platforms
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55091 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
fix build on no-fork-spawnv platforms
from argument vector in rb_execarg.
[ruby-core:75611] [Bug #12398]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55091 b2dd03c8-39d4-4d8f-98ff-823fe69b080e