[R] Avoid symbol naming conflicts with other packages (#7245)

* don't register all R symbols

* typo

R-package/src/init.c

@@ -9,6 +9,7 @@
 #include <Rinternals.h>
 #include <stdlib.h>
 #include <R_ext/Rdynload.h>
+#include <R_ext/Visibility.h>
 
 /* FIXME:
 Check these declarations against the C/Fortran source code.
@@ -89,7 +90,7 @@ static const R_CallMethodDef CallEntries[] = {
 #if defined(_WIN32)
 __declspec(dllexport)
 #endif  // defined(_WIN32)
-void R_init_xgboost(DllInfo *dll) {
+void attribute_visible R_init_xgboost(DllInfo *dll) {
   R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
   R_useDynamicSymbols(dll, FALSE);
 }