entries for C++26

git-svn-id: https://svn.r-project.org/R/trunk@87645 00db46b3-68df-0310-9c12-caf00c1e9a41

config.site

@@ -380,7 +380,7 @@
 
 ## C++23 compiler, optional for use in packages.
 ## Introduced in R 4.3.0
-## The command which runs the C++23 compiler: defaults to $(CXX17), but
+## The command which runs the C++23 compiler: defaults to $(CXX20), but
 ## empty if that (plus standard) cannot compile the tested C++23 code.
 ## CXX23=
 
@@ -396,6 +396,24 @@
 ## SHLIB_CXX23LD=
 ## SHLIB_CXX23LDFLAGS=
 
+## C++26 compiler, optional for use in packages.
+## Introduced in R 4.5.0
+## The command which runs the C++26 compiler: defaults to $(CXX20), but
+## empty if that (plus standard) cannot compile the tested C++26 code.
+## CXX26=
+
+## The 'standard' for the C++26 compiler, which is invoked as
+## $(CXX26) $(CXX26STD) for both compiling and linking DSOs/DLLs.  
+## '-std=gnu++26' and '-std=gnu++2a" are tried by configure, also
+## '-std=c++26' and '-std=c++2a"
+## CXX26STD=
+
+## Analogues for the C++26 compiler: default to the settings for C++17
+## CXX26FLAGS=
+## CXX26PICFLAGS=
+## SHLIB_CXX26LD=
+## SHLIB_CXX26LDFLAGS=
+
 ## Additional libraries to link the internet module against.
 ## Some claim Solaris needs -lsocket -lnsl
 ## INTERNET_LIBS=
@@ -427,7 +445,7 @@
 ## The configure code is conservative about enabling OpenMP 
 ## so use can be forced here (or non-use if set but empty).
 ## For packages (note that SHLIB_OPENMP_CXXFLAGS is for CXX, not
-## necessarily for CXX11/14/17/20/23).
+## necessarily for CXX11/14/17/20/23/26).
 ## SHLIB_OPENMP_CFLAGS=
 ## SHLIB_OPENMP_CXXFLAGS=
 ## SHLIB_OPENMP_FFLAGS=