Merge #17005: build: Qt version appears only if GUI is being built

57b0cd4db9 build: Installed Qt version only appears if being built (Jon Layton)

Pull request description:

  Closes #16989.

  Simplifies `./configure` output for `x$bitcoin_enable_qt`.

  Now:
  `checking whether to build Bitcoin Core GUI... no`
  `checking whether to build Bitcoin Core GUI... yes (Qt5)`

ACKs for top commit:
  laanwj:
    ACK 57b0cd4db9
  fanquake:
    ACK 57b0cd4db9

Tree-SHA512: 3ca2082f251c206bb1661277dac1075acea046f0a1d2cd997550aa83dd886036b7282f0e30cdaf51ed636d8a40d9b7ffb8600743450f4f4c014c541cb7b2eb0d

build-aux/m4/bitcoin_qt.m4

@@ -228,7 +228,11 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   ],[
     bitcoin_enable_qt=no
   ])
-  AC_MSG_RESULT([$bitcoin_enable_qt (Qt5)])
+  if test x$bitcoin_enable_qt = xyes; then
+    AC_MSG_RESULT([$bitcoin_enable_qt ($QT_LIB_PREFIX)])
+  else
+    AC_MSG_RESULT([$bitcoin_enable_qt])
+  fi
 
   AC_SUBST(QT_PIE_FLAGS)
   AC_SUBST(QT_INCLUDES)