define __VISUALCn__ for n=5,6,7,8,9 and not only 8; also document these symbols

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51353 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/cppconst.tex

@@ -149,7 +149,10 @@ to the compiler version: $500$ is $5.0$.}
 \twocolitem{\_\_VISAGECPP\_\_}{IBM Visual Age (OS/2)}
 \twocolitem{\_\_VISUALC\_\_}{Microsoft Visual C++. The value of this macro
 corresponds to the compiler version: $1020$ for $4.2$ (the first supported
-version), $1100$ for $5.0$, $1200$ for $6.0$ and so on}
+version), $1100$ for $5.0$, $1200$ for $6.0$ and so on. For convenience, the
+symbols \_\_VISUALCn\_\_ are also defined for each major compiler version from
+5 to 9, i.e. you can use tests such \texttt{#ifdef \_\_VISUALC7\_\_} to test
+for compiler version being precisely 7.}
 \twocolitem{\_\_XLC\_\_}{AIX compiler}
 \twocolitem{\_\_WATCOMC\_\_}{Watcom C++. The value of this macro corresponds to
 the compiler version, $1100$ is $11.0$ and $1200$ is OpenWatcom.}