[qtbase] Build ICU test with c++11. Contributes to JB#45300

Could have assumed this happening automatically, but apparently
the test doesn't pick up this config.

ICU now expect to have it for type declaration.

config.tests/unix/icu/icu.pro

@@ -1,5 +1,6 @@
 SOURCES = icu.cpp
 CONFIG += console
 CONFIG -= qt dylib
+CONFIG += c++11
 
 include($$PWD/../../../src/3rdparty/icu_dependency.pri)