corrections and clarifications

git-svn-id: https://svn.r-project.org/R/trunk@63539 00db46b3-68df-0310-9c12-caf00c1e9a41
need --whole-archive for libR.a

git-svn-id: https://svn.r-project.org/R/trunk@63541 00db46b3-68df-0310-9c12-caf00c1e9a41
Minor adjustments to code and comments in R_allocOrReuseVector.


git-svn-id: https://svn.r-project.org/R/trunk@63543 00db46b3-68df-0310-9c12-caf00c1e9a41