build, qt: Refactor internal _BITCOIN_QT_CHECK_STATIC_PLUGINS macro

This change puts Q_IMPORT_PLUGIN(...) boilerplate into the macro, which
now accepts only one plugin to check, and it is renamed (plural ->
singular).

build-aux/m4/bitcoin_qt.m4

@@ -111,9 +111,7 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   dnl For Qt5, we can check a header to find out whether Qt is build
   dnl statically. When Qt is built statically, some plugins must be linked into
   dnl the final binary as well.
-  dnl With Qt5, languages moved into core and the WindowsIntegration plugin was
-  dnl added.
-  dnl _BITCOIN_QT_CHECK_STATIC_PLUGINS does a quick link-check and appends the
+  dnl _BITCOIN_QT_CHECK_STATIC_PLUGIN does a quick link-check and appends the
   dnl results to QT_LIBS.
   BITCOIN_QT_CHECK([
   TEMP_CPPFLAGS=$CPPFLAGS
@@ -125,17 +123,17 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     _BITCOIN_QT_FIND_STATIC_PLUGINS
     AC_DEFINE(QT_STATICPLUGIN, 1, [Define this symbol if qt plugins are static])
     if test "x$TARGET_OS" != xandroid; then
-      _BITCOIN_QT_CHECK_STATIC_PLUGINS([Q_IMPORT_PLUGIN(QMinimalIntegrationPlugin)],[-lqminimal])
+      _BITCOIN_QT_CHECK_STATIC_PLUGIN([QMinimalIntegrationPlugin], [-lqminimal])
       AC_DEFINE(QT_QPA_PLATFORM_MINIMAL, 1, [Define this symbol if the minimal qt platform exists])
     fi
     if test "x$TARGET_OS" = xwindows; then
-      _BITCOIN_QT_CHECK_STATIC_PLUGINS([Q_IMPORT_PLUGIN(QWindowsIntegrationPlugin)],[-lqwindows])
+      _BITCOIN_QT_CHECK_STATIC_PLUGIN([QWindowsIntegrationPlugin], [-lqwindows])
       AC_DEFINE(QT_QPA_PLATFORM_WINDOWS, 1, [Define this symbol if the qt platform is windows])
     elif test "x$TARGET_OS" = xlinux; then
-      _BITCOIN_QT_CHECK_STATIC_PLUGINS([Q_IMPORT_PLUGIN(QXcbIntegrationPlugin)],[-lqxcb -lxcb-static])
+      _BITCOIN_QT_CHECK_STATIC_PLUGIN([QXcbIntegrationPlugin], [-lqxcb -lxcb-static])
       AC_DEFINE(QT_QPA_PLATFORM_XCB, 1, [Define this symbol if the qt platform is xcb])
     elif test "x$TARGET_OS" = xdarwin; then
-      _BITCOIN_QT_CHECK_STATIC_PLUGINS([Q_IMPORT_PLUGIN(QCocoaIntegrationPlugin)],[-lqcocoa])
+      _BITCOIN_QT_CHECK_STATIC_PLUGIN([QCocoaIntegrationPlugin], [-lqcocoa])
       AC_DEFINE(QT_QPA_PLATFORM_COCOA, 1, [Define this symbol if the qt platform is cocoa])
     elif test "x$TARGET_OS" = xandroid; then
       QT_LIBS="-Wl,--export-dynamic,--undefined=JNI_OnLoad -lqtforandroid -ljnigraphics -landroid -lqtfreetype -lQt5EglSupport $QT_LIBS"
@@ -284,22 +282,22 @@ AC_DEFUN([_BITCOIN_QT_IS_STATIC],[
     ])
 ])
 
-dnl Internal. Check if the link-requirements for static plugins are met.
+dnl Internal. Check if the link-requirements for a static plugin are met.
+dnl
+dnl _BITCOIN_QT_CHECK_STATIC_PLUGIN(PLUGIN, LIBRARIES)
+dnl --------------------------------------------------
+dnl
 dnl Requires: INCLUDES and LIBS must be populated as necessary.
-dnl Inputs: $1: A series of Q_IMPORT_PLUGIN().
+dnl Inputs: $1: A static plugin name.
 dnl Inputs: $2: The libraries that resolve $1.
 dnl Output: QT_LIBS is prepended or configure exits.
-AC_DEFUN([_BITCOIN_QT_CHECK_STATIC_PLUGINS],[
-  AC_MSG_CHECKING(for static Qt plugins: $2)
+AC_DEFUN([_BITCOIN_QT_CHECK_STATIC_PLUGIN], [
+  AC_MSG_CHECKING([for $1 ($2)])
   CHECK_STATIC_PLUGINS_TEMP_LIBS="$LIBS"
   LIBS="$2${qt_lib_suffix} $QT_LIBS $LIBS"
-  AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-    #define QT_STATICPLUGIN
-    #include <QtPlugin>
-    $1]],
-    [[return 0;]])],
-    [AC_MSG_RESULT(yes); QT_LIBS="$2${qt_lib_suffix} $QT_LIBS"],
-    [AC_MSG_RESULT(no); BITCOIN_QT_FAIL(Could not resolve: $2)])
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <QtPlugin> Q_IMPORT_PLUGIN($1)]])],
+    [AC_MSG_RESULT([yes]); QT_LIBS="$2${qt_lib_suffix} $QT_LIBS"],
+    [AC_MSG_RESULT([no]); BITCOIN_QT_FAIL([$1 not found.])])
   LIBS="$CHECK_STATIC_PLUGINS_TEMP_LIBS"
 ])