message: build: Fix Qt5PlatformSupport check without pkg-config
  The non-pkg-config case can't use pkg-config to check the version.
  Also, make sure that the check is properly guarded in the case of missing
  pkg-config macros.
diff: @@ -348,8 +348,9 @@ AC_DEFUN([_BITCOIN_QT_FIND_STATIC_PLUGINS],[
  QT_LIBS="$QT_LIBS -L$qt_plugin_path/accessible"
  fi
  fi
  - m4_ifdef([PKG_CHECK_MODULES],[
  if test x$use_pkgconfig = xyes; then
  + : dnl
  + m4_ifdef([PKG_CHECK_MODULES],[
  PKG_CHECK_MODULES([QTPLATFORM], [Qt5PlatformSupport], [QT_LIBS="$QTPLATFORM_LIBS $QT_LIBS"])
  if test x$TARGET_OS = xlinux; then
  PKG_CHECK_MODULES([X11XCB], [x11-xcb], [QT_LIBS="$X11XCB_LIBS $QT_LIBS"])
  @@ -359,12 +360,23 @@ AC_DEFUN([_BITCOIN_QT_FIND_STATIC_PLUGINS],[
  elif test x$TARGET_OS = xdarwin; then
  PKG_CHECK_MODULES([QTPRINT], [Qt5PrintSupport], [QT_LIBS="$QTPRINT_LIBS $QT_LIBS"])
  fi
  + ])
  else
  - if ${PKG_CONFIG} --exists "Qt5Core >= 5.6" 2>/dev/null; then
  - QT_LIBS="-lQt5PlatformSupport $QT_LIBS"
  + if test x$TARGET_OS = xwindows; then
  + AC_CACHE_CHECK(for Qt >= 5.6, bitcoin_cv_need_platformsupport,[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
  + [[#include <QtCore>]],[[
  + #if QT_VERSION < 0x050600
  + choke;
  + #endif
  + ]])],
  + [bitcoin_cv_need_platformsupport=yes],
  + [bitcoin_cv_need_platformsupport=no])
  + ])
  + if test x$bitcoin_cv_need_platformsupport = xyes; then
  + BITCOIN_QT_CHECK(AC_CHECK_LIB([${QT_LIB_PREFIX}PlatformSupport],[main],,BITCOIN_QT_FAIL(lib$QT_LIB_PREFIXPlatformSupport not found)))
  + fi
  fi
  fi
  - ])
  else
  if test x$qt_plugin_path != x; then
  QT_LIBS="$QT_LIBS -L$qt_plugin_path/accessible"
  