make lrelease only optionally bootstrapped

qt_tool.prf handles the magic for us.

Change-Id: Ifb8e7fd7ff0e46b9b274c9d156e048e89586ab2c
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/linguist/lrelease/lrelease.pro

 option(host_build)
-QT = bootstrap-private
+QT = core-private
 DEFINES += QT_NO_CAST_FROM_ASCII QT_NO_CAST_TO_ASCII
 
 SOURCES += main.cpp

src/linguist/shared/formats.pri

 
 # infrastructure
-!host_build: QT *= xml
+QT *= xml
 
 INCLUDEPATH *= $$PWD