[R-SIG-Mac] R CMD check warning in 4.0.0 RC

[Duncan Murdoch]

I've just installed R version 4.0.0 RC (2020-04-18 r78249) and am 
checking a package on MacOS High Sierra (10.13.6).  I can't install the 
recommended version of Xcode on this MacOS version.  I'm currently using 
Xcode 9.2.  (I think Xcode 10.x is supposed to work on High Sierra, but 
it isn't obvious how to update.)

My package has a small amount of C code, and R CMD check is clean, but R 
CMD check --as-cran gives this NOTE:

* checking compilation flags used ... NOTE
Compilation used the following non-portable flag(s):
   ‘-mmacosx-version-min=10.13’

I didn't supply that, it's the default, so probably this note should not 
appear (even though the message is true).

Duncan Murdoch