Reuse the provided dllname

[dfalbel]

We have a package that due to shared library name collisions we had to rename the generated .so to something else. In that case we rename it from torch.so to torchpkg.so.

A recent change in #133 uses a temporary file that has the same name as the package

https://github.com/r-lib/pkgload/pull/133/files#diff-33e8edea32dfc4630f62c402513e58979a315710778bc94dde36fb56c942a80eR92-R95

But this causes problems when the DLL being loaded doesn't have the same name as the R package.

This PR proposes to reuse the DLL name that was provided to library.dinam2 to fix the problem.

[jimhester]

Seems fine to me, @lionel-, it would be good if you could review this, and @dfalbel
can you please add a bullet to NEWS? It should briefly describe the change and end with (@yourname, #issuenumber).

[dfalbel]

Thanks @jimhester, added the NEWS bullet.

[lionel-]

Makes sense!

[jimhester]

Thanks @dfalbel for the PR and @lionel- for reviewing!

[krlmlr]

For reasons I don't fully understand, only this version works correctly with pillar on the M1. No action needed, except for a speedy CRAN release ;-)

With dev pkgload:

pkgload::load_all("~/git/R/pillar")
#> ℹ Loading pillar
tibble::tibble(a = 1)
#> # A tibble: 1 x 1
#>       a
#>   <dbl>
#> 1     1
pkgload::load_all("~/git/R/pillar")
#> ℹ Loading pillar
tibble::tibble(a = 1)
#> # A data frame: 1 × 1
#>       a
#>   <dbl>
#> 1     1

^{Created on 2021-06-05 by the reprex package (v2.0.0)}

With pkgload v1.2.1, either from CRAN or from a local clone:

pkgload::load_all("~/git/R/pillar")
#> ℹ Loading pillar
tibble::tibble(a = 1)
#> # A tibble: 1 x 1
#>       a
#>   <dbl>
#> 1     1
pkgload::load_all("~/git/R/pillar")
#> ℹ Loading pillar
tibble::tibble(a = 1)
#> # A data frame: 1 × 1
#>       a
#>   <dbl>
#> 1     1

^{Created on 2021-06-05 by the reprex package (v2.0.0)}

[krlmlr]

I stand corrected: both version behave the same, I'll file an issue.