Detect Watcom compiler version with its id

Decode decimal digits from __WATCOMC__ to compute the version number
components.  See documentation at:

  http://predef.sourceforge.net/precomp.html

Modules/CMakeCCompilerId.c.in

@@ -28,6 +28,8 @@
 
 #elif defined(__WATCOMC__)
 # define COMPILER_ID "Watcom"
+# define COMPILER_VERSION_MAJOR DEC(__WATCOMC__ / 100)
+# define COMPILER_VERSION_MINOR DEC(__WATCOMC__ % 100)
 
 #elif defined(__SUNPRO_C)
 # define COMPILER_ID "SunPro"

Modules/CMakeCXXCompilerId.cpp.in

@@ -30,6 +30,8 @@
 
 #elif defined(__WATCOMC__)
 # define COMPILER_ID "Watcom"
+# define COMPILER_VERSION_MAJOR DEC(__WATCOMC__ / 100)
+# define COMPILER_VERSION_MINOR DEC(__WATCOMC__ % 100)
 
 #elif defined(__SUNPRO_CC)
 # define COMPILER_ID "SunPro"