Previously it was not possible to define multiple ldflags, since only
the last definition applies, and there's some quoting issues with
`buildFlagsArray`. With the new `ldflags` argument it's possible to do
this, e.g.
ldflags = drv.ldflags or [] ++ [
"-X main.Version=1.0"
]
can now properly append a flag without clearing all previous ldflags.