Discover Qt paths using qmake (#26501)

* discover qt paths using qmake

* fix device build

* use subprocess.check_output

SConstruct

@@ -298,12 +298,15 @@ if arch == "Darwin":
   qt_env["FRAMEWORKS"] += [f"Qt{m}" for m in qt_modules] + ["OpenGL"]
   qt_env.AppendENVPath('PATH', os.path.join(qt_env['QTDIR'], "bin"))
 else:
-  qt_env['QTDIR'] = "/usr"
+  qt_install_prefix = subprocess.check_output(['qmake', '-query', 'QT_INSTALL_PREFIX'], encoding='utf8').strip()
+  qt_install_headers = subprocess.check_output(['qmake', '-query', 'QT_INSTALL_HEADERS'], encoding='utf8').strip()
+  
+  qt_env['QTDIR'] = qt_install_prefix
   qt_dirs = [
-    f"/usr/include/{real_arch}-linux-gnu/qt5",
-    f"/usr/include/{real_arch}-linux-gnu/qt5/QtGui/5.12.8/QtGui",
+    f"{qt_install_headers}",
+    f"{qt_install_headers}/QtGui/5.12.8/QtGui",
   ]
-  qt_dirs += [f"/usr/include/{real_arch}-linux-gnu/qt5/Qt{m}" for m in qt_modules]
+  qt_dirs += [f"{qt_install_headers}/Qt{m}" for m in qt_modules]
 
   qt_libs = [f"Qt5{m}" for m in qt_modules]
   if arch == "larch64":