Slightly more robust pull of .Machine entries

[MichaelChirico]

Related to #6153, getting longdouble.digits== is not the most helpful, I think there's a couple ways we could get that. I assume based on the base R code that we're seeing NULL there, but this will help clarify the actual value / rely less on inference.

[MichaelChirico]

format() will at least let us distinguish integer() from NULL.

[github-actions]

Generated via commit 2eeb415

Download link for the artifact containing the test results: ↓ atime-results.zip

Time taken to finish the standard R installation steps: 11 minutes and 44 seconds

Time taken to run atime::atime_pkg on the tests: 3 minutes and 18 seconds

[ben-schwen]

Maybe also add capabilities()["long.double"]?

[MichaelChirico]

I guess that's overkill, here's how that element of capabilities() is defined:

https://github.com/r-devel/r-svn/blob/e0f5c5e1c60bca2b7b2044eb0b4770e287cd770e/src/main/platform.c#L2627-L2628

Here's the LDOUBLE macro:

https://github.com/r-devel/r-svn/blob/1f537a2469956b505ad10135eeee282fe33a8475/src/include/Defn.h#L2407-L2411

In turn I think HAVE_LONG_DOUBLE gets set by ./configure.

Here's how .Machine$sizeof.longdouble is defined:

https://github.com/r-devel/r-svn/blob/1f537a2469956b505ad10135eeee282fe33a8475/src/main/machine.c#L139-L144

Here's the SIZEOF_LONG_DOUBLE macro:

https://github.com/r-devel/r-svn/blob/1f537a2469956b505ad10135eeee282fe33a8475/src/gnuwin32/fixed/h/config.h#L1182-L1191

So there might be some daylight between the two, WDYT?