Simplify bundled libjpeg build

Move the config headers of the bundled libjpeg back into its source
directory, where they originally live, to avoid having to trick with
the include path to find them.
The goal is unification across maintained Qt branches, making version
updates simpler.

Pick-to: 6.1 6.0 5.15 5.12
Change-Id: I5b574446bbd264b0a1cb3efceb4c1cb7203cac7d
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/3rdparty/libjpeg/import_from_libjpeg_tarball.sh

@@ -165,4 +165,4 @@ for i in $FILES; do
     copy_file "$i" "src/$i"
 done
 
-echo Done. $TARGET_DIR/jconfig.h and jconfigint.h may need manual updating.
+echo Done. $TARGET_DIR/src/jconfig.h and jconfigint.h may need manual updating.

src/plugins/imageformats/jpeg/CMakeLists.txt

@@ -90,7 +90,6 @@ qt_internal_extend_target(QJpegPlugin CONDITION NOT QT_FEATURE_system_jpeg
         ../../../3rdparty/libjpeg/src/jsimd_none.c
         ../../../3rdparty/libjpeg/src/jutils.c
     INCLUDE_DIRECTORIES
-        ../../../3rdparty/libjpeg
         ../../../3rdparty/libjpeg/src
 )