RStan toolchain error on ubuntu - r

Question

I installed RStan, had a problem, uninstalled it, and then tried reinstalling it using https://github.com/stan-dev/rstan/wiki/Installing-RStan-on-Mac-or-Linux
However, when I try using rstan, I get this error:
Error in library(rstan) : there is no package called ‘rstan’
I noticed when I run the toolchain diagnostic mentioned on the above page,
fx <- inline::cxxfunction( signature(x = "integer", y = "numeric" ) , '
return ScalarReal( INTEGER(x)[0] * REAL(y)[0] ) ;
' )
fx( 2L, 5 ) # should be 10
I get an error:
clang: warning: argument unused during compilation: '-arch x86_64'
clang: warning: argument unused during compilation: '-arch x86_64'
file16777e2261ec.o: file not recognized: File format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [file16777e2261ec.so] Error 1
ERROR(s) during compilation: source code errors or compiler configuration errors!
Program source:
1:
2: // includes from the plugin
3: #include <R.h>
4: #include <Rdefines.h>
5: #include <R_ext/Error.h>
6:
7:
8: // user includes
9:
10:
11: // declarations
12: extern "C" {
13: SEXP file16777e2261ec( SEXP x, SEXP y) ;
14: }
15:
16: // definition
17:
18: SEXP file16777e2261ec( SEXP x, SEXP y ){
19:
20: return ScalarReal( INTEGER(x)[0] * REAL(y)[0] ) ;
21:
22: Rf_warning("your C++ program does not return anything");
23: return R_NilValue ;
24: }
25:
26:
Error in compileCode(f, code, language = language, verbose = verbose) :
Compilation ERROR, function(s)/method(s) not created! clang: warning: argument unused during compilation: '-arch x86_64'
clang: warning: argument unused during compilation: '-arch x86_64'
file16777e2261ec.o: file not recognized: File format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [file16777e2261ec.so] Error 1
In addition: Warning message:
running command '/usr/lib/R/bin/R CMD SHLIB file16777e2261ec.cpp 2> file16777e2261ec.cpp.err.txt' had status 1
Error in fx(2L, 5) : could not find function "fx"
What is going wrong? Thank you!