use empty RCPP_CONSTEXPR if icc is used w/ C++98

Author: eddelbuettel

ChangeLog

@@ -1,6 +1,11 @@
+2017-02-01  Dirk Eddelbuettel  <edd@debian.org>
+
+        * inst/include/Rcpp/algorithm.h (RCPP_CONSTEXPR): Further refinement for
+        Intel compiler without C++11
+
 2017-01-31  Dirk Eddelbuettel  <edd@debian.org>
 
-        * DESCRIPTION (Date, Version): Roll minor version 
+        * DESCRIPTION (Date, Version): Roll minor version
 
         * inst/include/Rcpp/algorithm.h: Allow algorithm.h to be compiler under
         Intel's compiler, add copyright header and include guard

inst/include/Rcpp/algorithm.h

@@ -24,6 +24,8 @@
 
 #if __cplusplus >= 201103L || __INTEL_CXX11_MODE__ == 1
 #    define RCPP_CONSTEXPR constexpr
+#elif defined(__INTEL_COMPILER) 
+#    define RCPP_CONSTEXPR
 #else
 #    define RCPP_CONSTEXPR const
 #endif