Merge branch 'ab/deprecate-R-for-dynpath'

The way of specifying the path to find dynamic libraries at runtime has been simplified. The old default to pass -R/path/to/dir has been replaced with the new default to pass -Wl,-rpath,/path/to/dir, which is the more recent GCC uses. Those who need to build with an old GCC can still use "CC_LD_DYNPATH=-R" * ab/deprecate-R-for-dynpath: Makefile: remove the NO_R_TO_GCC_LINKER flag