Help: Clarify meaning of MSVC<NN> variables

They correspond to toolsets, not VS IDE versions.

Help/variable/MSVC10.rst

@@ -1,6 +1,5 @@
 MSVC10
 ------
 
-``True`` when using Microsoft Visual C++ 10.0
-
-Set to ``true`` when the compiler is version 10.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v100`` toolset
+(``cl`` version 16) or another compiler that simulates it.

Help/variable/MSVC11.rst

@@ -1,6 +1,5 @@
 MSVC11
 ------
 
-``True`` when using Microsoft Visual C++ 11.0
-
-Set to ``true`` when the compiler is version 11.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v110`` toolset
+(``cl`` version 17) or another compiler that simulates it.

Help/variable/MSVC12.rst

@@ -1,6 +1,5 @@
 MSVC12
 ------
 
-``True`` when using Microsoft Visual C++ 12.0.
-
-Set to ``true`` when the compiler is version 12.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v120`` toolset
+(``cl`` version 18) or another compiler that simulates it.

Help/variable/MSVC14.rst

@@ -1,6 +1,5 @@
 MSVC14
 ------
 
-``True`` when using Microsoft Visual C++ 14.0.
-
-Set to ``true`` when the compiler is version 14.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v140`` toolset
+(``cl`` version 19) or another compiler that simulates it.

Help/variable/MSVC80.rst

@@ -1,6 +1,5 @@
 MSVC80
 ------
 
-``True`` when using Microsoft Visual C++ 8.0.
-
-Set to ``true`` when the compiler is version 8.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v80`` toolset
+(``cl`` version 14) or another compiler that simulates it.

Help/variable/MSVC90.rst

@@ -1,6 +1,5 @@
 MSVC90
 ------
 
-``True`` when using Microsoft Visual C++ 9.0.
-
-Set to ``true`` when the compiler is version 9.0 of Microsoft Visual C++.
+``True`` when using the Microsoft Visual Studio ``v90`` toolset
+(``cl`` version 15) or another compiler that simulates it.