How to avoid “cannot find -lR” for R Package installation on windows

Related to: Installing source package - failure to link. Kevin Ushey gave the hint that it could be due to 32 vs 64 bit confusion and it could be due to pathes or sthg within the package. Following on this i made the pathes and package "reproducible / accessible).

First asked on #SO:

I want to install packages from source:

Setting up the environmental variables:

Sys.setenv(BINPREF = "C:/PROGRA~1/R/Rtools/mingw_64/bin/")
Sys.setenv(BINPREF64 = "C:/PROGRA~1/R/Rtools/mingw_64/bin/")
Sys.setenv(PATH = "C:/PROGRA~1/R/R-3.4.2/bin/x64/;C:/PROGRA~1/R/Rtools/bin/;C:/PROGRA~1/R/Rtools/mingw_64/bin/")

Installing any package from source results in "cannot find -lR" error:

install.packages("later")

Error message:

C:/PROGRA~1/R/Rtools/mingw_64/bin/g++ -shared -s -static-libgcc -o
later.dll tmp.def RcppExports.o callback_registry.o debug.o init.o
later.o later_posix.o later_win32.o timer_posix.o timestamp_unix.o
timestamp_win32.o tinycthread.o
-Ld:/Compiler/gcc-4.9.3/local330/lib/i386 -Ld:/Compiler/gcc-4.9.3/local330/lib -LC:/PROGRA~1/R/R-34~1.2/bin/i386 -lR C:/PROGRA~1/R/Rtools/mingw_64/bin/../lib/gcc/x86_64-w64-mingw32/4.9.3/../../../../x86_64-w64-mingw32/bin/ld.exe:
skipping incompatible C:/PROGRA~1/R/R-34~1.2/bin/i386/R.dll when searching for -lR
C:/PROGRA~1/R/Rtools/mingw_64/bin/../lib/gcc/x86_64-w64-mingw32/4.9.3/../../../../x86_64-w64-mingw32/bin/ld.exe:
skipping incompatible C:/PROGRA~1/R/R-34~1.2/bin/i386/R.dll when searching for -lR
C:/PROGRA~1/R/Rtools/mingw_64/bin/../lib/gcc/x86_64-w64-mingw32/4.9.3/../../../../x86_64-w64-mingw32/bin/ld.exe:
cannot find -lR collect2.exe: error: ld returned 1 exit status no DLL
was created
ERROR: compilation failed for package 'later'

My System info:
Sys.info()
sysname release version nodename machine login user effective_user
"Windows" "Server >= 2012 x64" "build 9200" "YY" "x86-64" "XX" "XX" "XX"

Session info:

Version:1.0 StartHTML:0000000107 EndHTML:0000001240 StartFragment:0000000127 EndFragment:0000001222

sessionInfo() R version 3.4.2 (2017-09-28) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows Server >= 2012 x64 (build 9200)

Rstudio 1.1.383