Patch retrieved from NixOS
https://github.com/NixOS/nixpkgs/blob/93ecdaa1f34354c9476062dc4fe323b442c087d5/pkgs/development/libraries/qt-6/patches/0003-qtbase-qmake-fix-includedir-in-generated-pkg-config.patch

From 6088085d3074316dd74639fc6c1233e5862aff11 Mon Sep 17 00:00:00 2001
From: Nick Cao <nickcao@nichi.co>
Date: Fri, 14 Apr 2023 09:34:46 +0800
Subject: [PATCH 03/11] qtbase: qmake: fix includedir in generated pkg-config

---
 qmake/generators/makefile.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/qmake/generators/makefile.cpp b/qmake/generators/makefile.cpp
index 11d2f0ff7df..c78ed0d3485 100644
--- a/qmake/generators/makefile.cpp
+++ b/qmake/generators/makefile.cpp
@@ -3412,8 +3412,7 @@ MakefileGenerator::writePkgConfigFile()
       << varGlue("QMAKE_PKGCONFIG_CFLAGS", "", " ", " ")
         //      << varGlue("DEFINES","-D"," -D"," ")
          ;
-    if (!project->values("QMAKE_DEFAULT_INCDIRS").contains(includeDir))
-        t << "-I${includedir}";
+    t << "-I${includedir}";
     if (target_mode == TARG_MAC_MODE && project->isActiveConfig("lib_bundle")
         && libDir != QLatin1String("/Library/Frameworks")) {
             t << " -F${libdir}";
-- 
2.42.0

