nixpkgs/pkgs/development/tools/misc/pkg-config/requires-private.patch

diff --git a/main.c b/main.c
index b61ca34..5a420c2 100644
--- a/main.c
+++ b/main.c
@@ -602,10 +602,10 @@ main (int argc, char **argv)
   else
     disable_private_libs();
 
-  /* honor Requires.private if any Cflags are requested or any static
+  /* honor Requires.private if any any static
    * libs are requested */
 
-  if (pkg_flags & CFLAGS_ANY || want_requires_private || want_exists ||
+  if (want_requires_private ||
       (want_static_lib_list && (pkg_flags & LIBS_ANY)))
     enable_requires_private();