message: set PRECOMPILED_HEADERS=true on Windows if CXX_MAJOR >= 8
diff: @@ -108,7 +108,11 @@ endif
  STAN_FLAGS=$(STAN_FLAG_THREADS)$(STAN_FLAG_MPI)$(STAN_FLAG_OPENCL)
  ifeq ($(OS),Windows_NT)
  +ifeq ($(shell expr $(CXX_MAJOR) \>= 8), 1)
  +PRECOMPILED_HEADERS ?= true
  +else
  PRECOMPILED_HEADERS ?= false
  +endif
  else
  PRECOMPILED_HEADERS ?= true
  endif
  