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 {
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<tr><td><span title='2018-06-13 09:11:45 +0200'>2018-06-13</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=c24b15472baaa7ec67d48cbf296bbe5ab727b78f'>tests: Honor the return value of 'start-service'.</a><span class='msg-avail'>...</span></td><td>Clément Lassieur</td></tr>
<tr><td><span title='2018-03-09 17:24:45 +0300'>2018-03-09</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=a9079b488037371f90514b82961dc075ea0b3985'>tests: mail: Add test for dovecot.</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2017-07-20 11:57:13 +0200'>2017-07-20</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=8b113790fa3bfd2300c737901ba161f079fedbdf'>tests: Use 'virtual-machine' records instead of monadic procedures.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-04-19 23:43:50 +0200'>2017-04-19</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=950026ac7f17b3b4d5420cde9709c24e9af76dcb'>tests: mail: Add test for exim</a><span class='msg-avail'>...</span></td><td>Carlo Zancanaro</td></tr>
<tr><td><span title='2017-04-01 00:45:18 +0200'>2017-04-01</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=892d9089a88abaa2ef1127f16308d03f4f08a4ce'>tests: Introduce 'simple-operating-system' and use it.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>