Merge #17547: build: Fix configure report about qr

651c636f9e build: Fix configure report about qr (Hennadii Stepanov)

Pull request description:

  On master (b7bc9b8330):
  ```
  $ apt list libqrencode-dev
  Listing... Done
  libqrencode-dev/bionic 3.4.4-1build1 amd64
  $ ./configure | grep -i qr
  checking for QR... no
  checking whether to build GUI with support for QR codes... no
      with qr     = auto
  ```

  With this PR:
  ```
  $ apt list libqrencode-dev
  Listing... Done
  libqrencode-dev/bionic 3.4.4-1build1 amd64
  $ ./configure | grep -i qr
  checking for QR... no
  checking whether to build GUI with support for QR codes... no
      with qr     = no
  ```

ACKs for top commit:
  laanwj:
    Concept and light code review ACK 651c636f9e
  fanquake:
    ACK 651c636f9e

Tree-SHA512: 8959b1c7da5b28d06affcdd27ff4e455f1f7d9c8363dbde8ef07aaf79139ec8bc7ce25610b28e1d90c7e168573ee90ac9ab359bf10c667d0254507f8a880a935

configure.ac

@@ -1471,18 +1471,16 @@ if test x$bitcoin_enable_qt != xno; then
   AC_MSG_CHECKING([whether to build GUI with support for QR codes])
   if test x$have_qrencode = xno; then
     if test x$use_qr = xyes; then
-     AC_MSG_ERROR("QR support requested but cannot be built. use --without-qrencode")
+      AC_MSG_ERROR([QR support requested but cannot be built. Use --without-qrencode])
     fi
-    AC_MSG_RESULT(no)
+    use_qr=no
   else
     if test x$use_qr != xno; then
-      AC_MSG_RESULT(yes)
       AC_DEFINE([USE_QRCODE],[1],[Define if QR support should be compiled in])
       use_qr=yes
-    else
-      AC_MSG_RESULT(no)
     fi
   fi
+  AC_MSG_RESULT([$use_qr])
 
   if test x$XGETTEXT = x; then
     AC_MSG_WARN("xgettext is required to update qt translations")