include/openssl: don't include <windows.h> in public headers.

If application uses any of Windows-specific interfaces, make it
application developer's respondibility to include <windows.h>.
Rationale is that <windows.h> is quite "toxic" and is sensitive
to inclusion order (most notably in relation to <winsock2.h>).
It's only natural to give complete control to the application developer.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>

util/mkdef.pl

diff --git a/util/mkdef.pl b/util/mkdef.pl
index c2fbfe7..fa37ccb 100755
--- a/util/mkdef.pl
+++ b/util/mkdef.pl
@@ -73,7 +73,7 @@
 my $safe_stack_def = 0;
 
 my @known_platforms = ( "__FreeBSD__", "PERL5",
-			"EXPORT_VAR_AS_FUNCTION", "ZLIB"
+			"EXPORT_VAR_AS_FUNCTION", "ZLIB", "_WIN32"
 			);
 my @known_ossl_platforms = ( "VMS", "WIN32", "WINNT", "OS2" );
 my @known_algorithms = ( "RC2", "RC4", "RC5", "IDEA", "DES", "BF",
@@ -1121,6 +1121,7 @@
 			if ($keyword eq "VMSNonVAX" && $VMSNonVAX) { return 1; }
 			if ($keyword eq "VMS" && $VMS) { return 1; }
 			if ($keyword eq "WIN32" && $W32) { return 1; }
+			if ($keyword eq "_WIN32" && $W32) { return 1; }
 			if ($keyword eq "WINNT" && $NT) { return 1; }
 			# Special platforms:
 			# EXPORT_VAR_AS_FUNCTION means that global variables