Undo a90081576c94f9f54de1755188a00ccc1760549a

Undo unapproved commit that removed DJGPP and WATT32
diff --git a/e_os2.h b/e_os2.h
index d07c4b9..f4597a2 100644
--- a/e_os2.h
+++ b/e_os2.h
@@ -85,7 +85,7 @@
 /* ---------------------- Microsoft operating systems ---------------------- */
 
 /* Note that MSDOS actually denotes 32-bit environments running on top of
-   MS-DOS. */
+   MS-DOS, such as DJGPP one. */
 #if defined(OPENSSL_SYSNAME_MSDOS)
 # undef OPENSSL_SYS_UNIX
 # define OPENSSL_SYS_MSDOS