SDL: wikiheaders.pl: Put the manpages in man/man3

SDL Commits
1 
From f62b807174c2b0e30fc9f12878939510c579e22e Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Fri, 7 Jan 2022 21:31:38 -0500
Subject: [PATCH] wikiheaders.pl: Put the manpages in man/man3

---
 build-scripts/wikiheaders.pl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/build-scripts/wikiheaders.pl b/build-scripts/wikiheaders.pl
index 1259087be53..2be760cac67 100755
--- a/build-scripts/wikiheaders.pl
+++ b/build-scripts/wikiheaders.pl
@@ -1057,6 +1057,8 @@ sub usage {
 
     my $manpath = "$srcpath/man";
     mkdir($manpath);
+    $manpath .= "/man3";
+    mkdir($manpath);
 
     $dewikify_mode = 'manpage';
     $wordwrap_mode = 'manpage';