gnu: qt-4: Do not set $LDFLAGS since that triggerred a build failure.

Fixes the build failure at <http://hydra.gnu.org/build/379884/log/raw>:

  g++ -licui18n -Wl,-O1 [...] -o ../../../../bin/assistant [...]
  ld: warning: libQtCLucene.so.4, needed by /tmp/nix-build-qt-4.8.6.drv-0/qt-everywhere-opensource-src-4.8.6/lib/libQtHelp.so, not found (try using -rpath or -rpath-link)
  /tmp/nix-build-qt-4.8.6.drv-0/qt-everywhere-opensource-src-4.8.6/lib/libQtHelp.so: undefined reference to `QCLucenePhraseQuery::getTerms() const'
  [...]

* gnu/packages/patches/qt4-ldflags.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/qt.scm (qt-4)[source]: Use it.
  [arguments]: Remove 'setenv' call in 'configure' phase.

gnu-system.am

@@ -520,6 +520,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/python2-rdflib-drop-sparqlwrapper.patch	\
   gnu/packages/patches/python2-sqlite-3.8.4-test-fix.patch	\
   gnu/packages/patches/python2-pygobject-2-gi-info-type-error-domain.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/qt4-ldflags.patch

@@ -0,0 +1,18 @@
+Explicitly link against libicui18n so that libQtCore.so always finds it.
+
+--- qt-everywhere-opensource-src-4.8.6/src/corelib/corelib.pro	2015-04-15 12:01:41.661862663 +0200
++++ qt-everywhere-opensource-src-4.8.6/src/corelib/corelib.pro	2015-04-15 12:03:57.954586336 +0200
+@@ -19,6 +19,13 @@ include(codecs/codecs.pri)
+ include(statemachine/statemachine.pri)
+ include(xml/xml.pri)
+ 
++# Explicitly link with icui18n, which is dlopened by libQtCore.so.
++# We cannot do this by setting LDFLAGS because that then overrides
++# other LDFLAGS: <https://bugreports.qt.io/browse/QTBUG-5471>.
++# XXX: According to the Nixpkgs recipe, this may be necessary for
++# further libraries (cups, gtk-x11-2.0, libgdk-x11-2.0).
++LIBS_PRIVATE += -licui18n
++
+ !qpa:mac|darwin:LIBS_PRIVATE += -framework ApplicationServices
+ qpa:mac {
+     !ios {

gnu/packages/qt.scm

@@ -230,7 +230,8 @@ developers using C++ or QML, a CSS & JavaScript like language.")
              (sha256
               (base32
                "0b036iqgmbbv37dgwwfihw3mihjbnw3kb5kaisdy0qi8nn8xs54b"))
-             (patches (list (search-patch "qt4-tests.patch")))))
+             (patches (map search-patch
+                           '("qt4-ldflags.patch" "qt4-tests.patch")))))
     (inputs `(,@(alist-delete "libjpeg" (package-inputs qt))
               ("libjepg" ,libjpeg-8)
               ("libsm" ,libsm)))
@@ -241,15 +242,8 @@ developers using C++ or QML, a CSS & JavaScript like language.")
           (lambda* (#:key outputs #:allow-other-keys)
             (let ((out (assoc-ref outputs "out")))
               (substitute* '("configure")
-                           (("/bin/pwd") (which "pwd")))
-              ;; Explicitly link with icui18n, which is dlopened by
-              ;; QtCore.so. The LDFLAGS are in fact added to other flags
-              ;; determined by the configure phase.
-              ;; According to the nix recipe, this may be necessary for
-              ;; further libraries (cups, gtk-x11-2.0, libgdk-x11-2.0).
-              (setenv "LDFLAGS" "-licui18n")
-              ;; do not pass "--enable-fast-install", which makes the
-              ;; configure process fail
+                (("/bin/pwd") (which "pwd")))
+
               (zero? (system*
                       "./configure"
                       "-verbose"