[gimp] Revert "libgimp: gimpdb-private.h was removed."

[Michael Natterer <mitch src gnome org>]

commit f8895f7f229e817395740400216950ea67b558e3
Author: Michael Natterer <mitch gimp org>
Date:   Wed Aug 14 20:44:36 2019 +0200

    Revert "libgimp: gimpdb-private.h was removed."
    
    It's very much alive :)
    
    This reverts commit e67c922b000b42691e2cf1d6cdd988c2badc842e.

 libgimp/Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/libgimp/Makefile.am b/libgimp/Makefile.am
index 97ff63dd10..4d4882b0fe 100644
--- a/libgimp/Makefile.am
+++ b/libgimp/Makefile.am
@@ -116,6 +116,7 @@ libgimp_private_sources = \
        gimplegacy.c            \
        gimplegacy.h            \
        gimplegacy-private.h    \
+       gimpdb-private.h        \
        gimppdbprocedure.c      \
        gimppdbprocedure.h      \
        gimppixbuf.c            \