Building R package with integrate_ode_bdf() results in `Symbol not found: _CVode`

Summary:

If I try to build an R package that uses rstan and includes the BDF ODE solver (integrate_ode_bdf), I receive the error Symbol not found: _CVode.

Description:

• I am unable to build R packages that use the integrate_ode_bdf ODE solver using the set up as built by rstantools.
• The integrate_ode_rk45 ODE solver works.
• I can also build rstan models that use integrate_ode_bdf through rstan::stan_model or rstan::stan outside of an R package structure.
• I have posted a minimal R package in a GitHub repo below as an example.
• I'm not sure if this is an rstan or rstantools issue. If this should be an rstantools issue this could be moved there or this can be closed and I will repost.

Reproducible Steps:

Try to install this minimal package I put together using rstantools::rstan_create_package() and an example from the Stan manual:

remotes::install_github("seananderson/testBDF")

Current Output:

Error: package or namespace load failed for ‘testBDF’ in dyn.load(file, DLLpath = DLLpath, ...):
 unable to load shared object '/Library/Frameworks/R.framework/Versions/4.0/Resources/library/00LOCK-testBDF/00new/testBDF/libs/testBDF.so':
  dlopen(/Library/Frameworks/R.framework/Versions/4.0/Resources/library/00LOCK-testBDF/00new/testBDF/libs/testBDF.so, 6): Symbol not found: _CVode
  Referenced from: /Library/Frameworks/R.framework/Versions/4.0/Resources/library/00LOCK-testBDF/00new/testBDF/libs/testBDF.so
  Expected in: flat namespace
 in /Library/Frameworks/R.framework/Versions/4.0/Resources/library/00LOCK-testBDF/00new/testBDF/libs/testBDF.so
Error: loading failed
Execution halted

I assume the important error is Symbol not found: _CVode

The above was on OS X as described below. On Windows R 3.6.2 I've been told the error is:

undefined reference to `CVodeFree' collect2.exe: error: ld returned 1 exit status

Expected Output:

The package to build and install. The package will build and install if integrate_ode_bdf is replaced with integrate_ode_rk45.

RStan Version:

rstan: 2.21.2
StanHeaders: 2.21.0.5
rstantools: 2.1.1 or 2.1.1.9000

R Version:

R version 4.0.2 (2020-06-22)

(Also tested on Windows R 3.6.2)

Operating System:

OS X 10.15.6

(Also tested on Windows 10 1909)

Reproduce the failure by installing the minimal testBDF package generated with rstantools::rstan_create_package(), using integrate_ode_bdf and then integrate_ode_rk45 for comparison. Trace the package build and linking setup around the missing CVode and CVodeFree symbols on macOS and Windows; done means the BDF-based package builds and installs successfully.