Update docs

Author: petk

docs/cmake/differences.md

@@ -112,6 +112,9 @@ build system:
 
 * HP-UX platform is not supported in CMake-based build system anymore.
 
+* On Windows, there is also `main/build-defs.h` header added and included in the
+  `main/config.w32.h` to be synced with \*nix configuration.
+
 ## Bugs fixed
 
 * Building inside folder with spaces.

docs/cmake/modules/FindSendmail.md

@@ -11,8 +11,9 @@ either `sendmail` is used if found, or a general default value is set to
 ## Result variables
 
 * `Sendmail_FOUND` - Whether sendmail has been found.
-* `PROG_SENDMAIL` - Path to the sendmail executable program, either found by
-  the module or set to a sensible default value.
+* `Sendmail_PROGRAM` - Path to the sendmail executable program, either found by
+  the module or set to a sensible default value for usage in PHP. On Windows,
+  this is set to an empty string as PHP uses a built in mailer there.
 
 ## Cache variables