[Rd] configure script issue with -flto with recent gcc and system ar/ranlib

[Thomas König]

Hi,

there can be an issue with recent gcc where the system-installed "ar"
and "ranlib" commands cannot handle LTO binaries.  On compilation, this
manifests itself with error messages claiming that they need extra
plugins.

This can be fixed by using the command line

$ AR=gcc-ar RANLIB=gcc-ranlib ./configure --enable-lto

so it is not a big issue, but it would still be nicer if the configure
script tested the functionality of ar and ranlib itself and would
select the appropriate one accordingly.

This is with R version 3.5.3.

Regards

	Thomas