SDL: cmake: fix header GLOB used for generating man pages

From 1061a978c3d44b17aa2daa2d76d6161ce6af4deb Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Tue, 27 Jun 2023 13:49:29 +0200
Subject: [PATCH] cmake: fix header GLOB used for generating man pages

---
 cmake/sdlmanpages.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/sdlmanpages.cmake b/cmake/sdlmanpages.cmake
index 12593d29377f..c9992b0c2e77 100644
--- a/cmake/sdlmanpages.cmake
+++ b/cmake/sdlmanpages.cmake
@@ -32,7 +32,7 @@ function(SDL_generate_manpages)
   set(BUILD_MANDIR "${ARG_BUILD_DOCDIR}/man")
 
   find_package(Perl)
-  file(GLOB HEADER_FILES "${HEADERS_DIR}/*.h")
+  file(GLOB HEADER_FILES "${ARG_HEADERS_DIR}/*.h")
 
   set(result FALSE)