diff -rupN --no-dereference qtbase-everywhere-src-5.12.5/qmake/generators/makefile.cpp qtbase-everywhere-src-5.12.5-new/qmake/generators/makefile.cpp
--- qtbase-everywhere-src-5.12.5/qmake/generators/makefile.cpp	2019-09-25 09:47:34.131552768 +0200
+++ qtbase-everywhere-src-5.12.5-new/qmake/generators/makefile.cpp	2019-09-25 09:47:34.134552760 +0200
@@ -3246,6 +3246,9 @@ MakefileGenerator::pkgConfigFileName(boo
         if (dot != -1)
             ret = ret.left(dot);
     }
+    if (project->isActiveConfig("debug")) {
+        ret += "d";
+    }
     ret += Option::pkgcfg_ext;
     QString subdir = project->first("QMAKE_PKGCONFIG_DESTDIR").toQString();
     if(!subdir.isEmpty()) {