Detect IBM XL compiler version with its id

Decode decimal digits from __IBMC__ and __IBMCPP__ to compute version
number components.  See documentation at:

  http://predef.sourceforge.net/precomp.html
  http://publib.boulder.ibm.com/infocenter/comphelp/v111v131/topic/com.ibm.xlc111.aix.doc/compiler_ref/xlmacros.html
  http://publib.boulder.ibm.com/infocenter/comphelp/v111v131/topic/com.ibm.xlcpp111.aix.doc/compiler_ref/xlmacros.html

Modules/CMakeCCompilerId.c.in

@@ -38,11 +38,16 @@
 #elif defined(__IBMC__)
 # if defined(__COMPILER_VER__)
 #  define COMPILER_ID "zOS"
-# elif __IBMC__ >= 800
+# else
+#  if __IBMC__ >= 800
 #   define COMPILER_ID "XL"
 #  else
 #   define COMPILER_ID "VisualAge"
 #  endif
+#  define COMPILER_VERSION_MAJOR DEC(__IBMC__/100)
+#  define COMPILER_VERSION_MINOR DEC(__IBMC__/10 % 10)
+#  define COMPILER_VERSION_PATCH DEC(__IBMC__    % 10)
+# endif
 
 #elif defined(__PGI)
 # define COMPILER_ID "PGI"

Modules/CMakeCXXCompilerId.cpp.in

@@ -40,11 +40,16 @@
 #elif defined(__IBMCPP__)
 # if defined(__COMPILER_VER__)
 #  define COMPILER_ID "zOS"
-# elif __IBMCPP__ >= 800
+# else
+#  if __IBMCPP__ >= 800
 #   define COMPILER_ID "XL"
 #  else
 #   define COMPILER_ID "VisualAge"
 #  endif
+#  define COMPILER_VERSION_MAJOR DEC(__IBMCPP__/100)
+#  define COMPILER_VERSION_MINOR DEC(__IBMCPP__/10 % 10)
+#  define COMPILER_VERSION_PATCH DEC(__IBMCPP__    % 10)
+# endif
 
 #elif defined(__PGI)
 # define COMPILER_ID "PGI"