configure: fix processing of *_LIBS_{DEBUG|RELEASE}= args

qtConfLibrary_inline() used to set $${1}.builds.$${b}.libs, while
everything else assumed no such .libs suffix. fix the former.

amends 9172143f52.

Task-number: QTBUG-61431
Started-by: Konstantin Ritt <ritt.ks@gmail.com>
Change-Id: I0bd81591c46266d81baa9c12315411183bbc7a63
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

mkspecs/features/qt_configure.prf

@@ -513,8 +513,8 @@ defineTest(qtConfLibrary_inline) {
         iv = $${input}.libs.$${b}
         vars += $$eval(config.commandline.rev_assignments.$${iv})
         defined(config.input.$${iv}, var) {
-            $${1}.builds.$${b}.libs = $$eval(config.input.$${iv})
-            export($${1}.builds.$${b}.libs)
+            $${1}.builds.$${b} = $$eval(config.input.$${iv})
+            export($${1}.builds.$${b})
             any = true
         } else {
             all = false