gnu: qt-4: Disable webkit build.

* gnu/packages/qt.scm (qt-4)[source]: Add snippet to remove the webkit code
  and drop one patch used previously for webkit.
  [arguments]: Add configure flag to disable building the webkit module.
* gnu/packages/patches/qt4-tests.patch: Delete file.
* gnu-system.am (dist_patch_DATA): Unregister patch.

Partially fixes <http://bugs.gnu.org/21288>.

gnu-system.am

@@ -611,7 +611,6 @@ dist_patch_DATA =						\
   gnu/packages/patches/python2-pygobject-2-gi-info-type-error-domain.patch \
   gnu/packages/patches/qemu-CVE-2015-6855.patch			\
   gnu/packages/patches/qt4-ldflags.patch			\
-  gnu/packages/patches/qt4-tests.patch				\
   gnu/packages/patches/qt5-runpath.patch			\
   gnu/packages/patches/ratpoison-shell.patch			\
   gnu/packages/patches/readline-link-ncurses.patch		\

gnu/packages/patches/qt4-tests.patch

@@ -1,22 +0,0 @@
-Drop tests requiring a running X server, but not starting any.
-
-diff -ru qt-everywhere-opensource-src-4.8.5.orig/src/3rdparty/webkit/Source/WebKit/qt/tests/tests.pro qt-everywhere-opensource-src-4.8.5/src/3rdparty/webkit/Source/WebKit/qt/tests/tests.pro
---- qt-everywhere-opensource-src-4.8.5.orig/src/3rdparty/webkit/Source/WebKit/qt/tests/tests.pro	2013-10-12 13:15:47.000000000 +0200
-+++ qt-everywhere-opensource-src-4.8.5/src/3rdparty/webkit/Source/WebKit/qt/tests/tests.pro	2013-10-12 13:20:15.000000000 +0200
-@@ -1,15 +1,4 @@
- 
- TEMPLATE = subdirs
--SUBDIRS = qwebframe qwebpage qwebelement qgraphicswebview qwebhistoryinterface qwebview qwebhistory qwebinspector hybridPixmap
-+SUBDIRS =
- 
--linux-* {
--    # This test bypasses the library and links the tested code's object itself.
--    # This stresses the build system in some corners so we only run it on linux.
--    SUBDIRS += MIMESniffing
--}
--
--contains(QT_CONFIG, declarative): SUBDIRS += qdeclarativewebview
--SUBDIRS += benchmarks/painting benchmarks/loading
--contains(DEFINES, ENABLE_WEBGL=1) {
--    SUBDIRS += benchmarks/webgl
--}

gnu/packages/qt.scm

@@ -243,7 +243,11 @@ developers using C++ or QML, a CSS & JavaScript like language.")
               (base32
                "183fca7n7439nlhxyg1z7aky0izgbyll3iwakw4gwivy16aj5272"))
              (patches (map search-patch
-                           '("qt4-ldflags.patch" "qt4-tests.patch")))))
+                           '("qt4-ldflags.patch")))
+             (modules '((guix build utils)))
+             (snippet
+              ;; Remove webkit module, which is not built.
+              '(delete-file-recursively "src/3rdparty/webkit"))))
     (inputs `(,@(alist-delete "harfbuzz"
                               (alist-delete "libjpeg" (package-inputs qt)))
               ("libjepg" ,libjpeg-8)
@@ -288,6 +292,9 @@ developers using C++ or QML, a CSS & JavaScript like language.")
                       "-confirm-license"
                       ;; explicitly link with dbus instead of dlopening it
                       "-dbus-linked"
+                      ;; Skip the webkit module; it fails to build on armhf
+                      ;; and, apart from that, may pose security risks.
+                      "-no-webkit"
                       ;; drop special machine instructions not supported
                       ;; on all instances of the target
                       ,@(if (string-prefix? "x86_64"