R CMD config CXXCPP has been deprecated: it is not used by R itself and there are several things wrong with the standard autoconf detection code:
If CXXCPP is set by the user, it is not tested. It could be empty, which AFAICS none of you allow for.
The code looks at $CXX -E and /lib/cpp in turn, and tests a system C header without consulting CPPFLAGS. /lib/cpp is unlikely to find C++ headers, and we have seen instances where without CPPFLAGS it did not find C headers.
It is the setting for the default C++ compiler, in R-devel C++11 but not specified in earlier R (even 3.6.x could be C++98).
It would be better to use $(CXX) -E (or $(CXX11) etc) or test for yourself.
From Brian Ripley:
via R CMD config.
This concerns packages
RPEIF SplitReg V8 arrow av cld3 dfmeta freetypeharfbuzz gaselect nloptr odbc opencv pdftools pense protolite rzmq stringi tesseract
R CMD config CXXCPP has been deprecated: it is not used by R itself and there are several things wrong with the standard autoconf detection code:
It would be better to use $(CXX) -E (or $(CXX11) etc) or test for yourself.
Please change at the next package update.