bitcoin_qt.m4: Improve QT_VERSION tests.

Use '<QtCore/qconfig.h> and '<QtCore/qglobal.h>' for testing QT_VERSION.
This makes the tests work with both Qt4 and Qt5, even if '-fPIC' or '-fPIE'
is not used (the compiler might choke otherwise if QT_REDUCE_RELOCATIONS is
active).

build-aux/m4/bitcoin_qt.m4

@@ -118,10 +118,16 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     if test x$bitcoin_cv_static_qt = xyes; then
       _BITCOIN_QT_FIND_STATIC_PLUGINS
       AC_DEFINE(QT_STATICPLUGIN, 1, [Define this symbol if qt plugins are static])
-      AC_CACHE_CHECK(for Qt < 5.4, bitcoin_cv_need_acc_widget,[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
-          [[#include <QtCore>]],[[
+      AC_CACHE_CHECK(for Qt < 5.4, bitcoin_cv_need_acc_widget,[
+        AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+            #include <QtCore/qconfig.h>
+            #ifndef QT_VERSION
+            #  include <QtCore/qglobal.h>
+            #endif
+          ]],
+          [[
             #if QT_VERSION >= 0x050400
-          choke;
+            choke
             #endif
           ]])],
         [bitcoin_cv_need_acc_widget=yes],
@@ -173,10 +179,15 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     TEMP_CXXFLAGS=$CXXFLAGS
     CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
     CXXFLAGS="$PIE_FLAGS $CXXFLAGS"
-    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <QtCore/qconfig.h>]],
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+        #include <QtCore/qconfig.h>
+        #ifndef QT_VERSION
+        #  include <QtCore/qglobal.h>
+        #endif
+      ]],
       [[
         #if defined(QT_REDUCE_RELOCATIONS)
-              choke;
+        choke
         #endif
       ]])],
       [ AC_MSG_RESULT(yes); QT_PIE_FLAGS=$PIE_FLAGS ],
@@ -190,10 +201,15 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     AC_MSG_CHECKING(whether -fPIC is needed with this Qt config)
     TEMP_CPPFLAGS=$CPPFLAGS
     CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
-    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <QtCore/qconfig.h>]],
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+        #include <QtCore/qconfig.h>
+        #ifndef QT_VERSION
+        #  include <QtCore/qglobal.h>
+        #endif
+      ]],
       [[
         #if defined(QT_REDUCE_RELOCATIONS)
-              choke;
+        choke
         #endif
       ]])],
       [ AC_MSG_RESULT(no)],
@@ -269,13 +285,15 @@ dnl Requires: INCLUDES must be populated as necessary.
 dnl Output: bitcoin_cv_qt5=yes|no
 AC_DEFUN([_BITCOIN_QT_CHECK_QT5],[
   AC_CACHE_CHECK(for Qt 5, bitcoin_cv_qt5,[
-  AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
-    [[#include <QtCore>]],
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+      #include <QtCore/qconfig.h>
+      #ifndef QT_VERSION
+      #  include <QtCore/qglobal.h>
+      #endif
+    ]],
     [[
       #if QT_VERSION < 0x050000
-      choke me
-      #else
-      return 0;
+      choke
       #endif
     ]])],
     [bitcoin_cv_qt5=yes],
@@ -289,13 +307,15 @@ dnl Output: bitcoin_cv_static_qt=yes|no
 dnl Output: Defines QT_STATICPLUGIN if plugins are static.
 AC_DEFUN([_BITCOIN_QT_IS_STATIC],[
   AC_CACHE_CHECK(for static Qt, bitcoin_cv_static_qt,[
-  AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
-    [[#include <QtCore>]],
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+      #include <QtCore/qconfig.h>
+      #ifndef QT_VERSION
+      #  include <QtCore/qglobal.h>
+      #endif
+    ]],
     [[
-      #if defined(QT_STATIC)
-      return 0;
-      #else
-      choke me
+      #if !defined(QT_STATIC)
+      choke
       #endif
     ]])],
     [bitcoin_cv_static_qt=yes],
@@ -352,10 +372,16 @@ AC_DEFUN([_BITCOIN_QT_FIND_STATIC_PLUGINS],[
      ])
      else
        if test x$TARGET_OS = xwindows; then
-         AC_CACHE_CHECK(for Qt >= 5.6, bitcoin_cv_need_platformsupport,[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
-             [[#include <QtCore>]],[[
+         AC_CACHE_CHECK(for Qt >= 5.6, bitcoin_cv_need_platformsupport,[
+           AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+               #include <QtCore/qconfig.h>
+               #ifndef QT_VERSION
+               #  include <QtCore/qglobal.h>
+               #endif
+             ]],
+             [[
                #if QT_VERSION < 0x050600
-             choke;
+               choke
                #endif
              ]])],
            [bitcoin_cv_need_platformsupport=yes],