more on OpenMP versions

git-svn-id: https://svn.r-project.org/R/trunk@70839 00db46b3-68df-0310-9c12-caf00c1e9a41

doc/manual/R-admin.texi

@@ -4624,7 +4624,7 @@ project (@url{http://libcxx.llvm.org/}) has also been tested: for some
 
 Most builds of @command{clang} have no OpenMP support.  Builds of
 version 3.7.0 or later may.@footnote{This also needs the OpenMP runtime,
-which is usually distributed separately, e.g.@: at
+which has sometimes been distributed separately, e.g.@: for 3.7.0 at
 @uref{http://llvm.org/releases}.}
 
 @node Intel compilers, Oracle Solaris Studio compilers, Clang, Linux
@@ -4795,7 +4795,8 @@ More recent and complete distributions of @command{clang} are usually
 available from @uref{http://llvm.org/releases/}.  In particular, these
 include support for the `Address Sanitizer' (not included by Apple until
 Xcode 7) and for OpenMP@footnote{This also needs the OpenMP runtime,
-which is distributed separately at that site.} in version 3.7.0 and later.
+which was distributed separately at that site for 3.7.0.} in version
+3.7.0 and later.
 
 Pre-compiled versions of many of the @ref{Useful libraries and programs}
 are available from @uref{https://r.research.att.com/libs/}.  You will

doc/manual/R-exts.texi

@@ -2073,12 +2073,17 @@ PKG_LIBS = $(SHLIB_OPENMP_CFLAGS)
 as the C compiler will be used to link the package code (and there is no
 guarantee that this will work everywhere).
 
-
-There is nothing to say what version of OpenMP is supported: version 3.0
-(May 2008) is supported by recent versions of the Linux, Windows and
-Solaris platforms, but portable packages cannot assume that end users
-have recent versions.  macOS currently uses Apple builds of
-@command{clang} with no OpenMP support.
+@c http://openmp.org/wp/openmp-compilers/
+@c clang 3.8.x reports 201307 but has full suport only for 3.1 (201111)
+There is nothing@footnote{In most implementations the
+@code{_OPENMP} macro has value a date which can be mapped to an OpenMP
+version: for example, value @code{201307} is the date of version 4.0
+(July 2013). However this may be used to denote the latest version which
+is partially supported, not that which is fully implemented.}  to say
+what version of OpenMP is supported: version 3.1 is supported by recent
+versions of the Linux, Windows and Solaris platforms, but portable
+packages cannot assume that end users have recent versions.  macOS
+currently uses Apple builds of @command{clang} with no OpenMP support.
 
 The performance of OpenMP varies substantially between platforms.  Both
 the Windows and earlier Apple macOS implementations have substantial