Fix locale generation for win32 builds

Closes #2577

.travis/linux.win32.install.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-PACKAGES="nsis cloog-isl libmpc2 mingw32
+PACKAGES="nsis cloog-isl libmpc2 qt4-linguist-tools mingw32
 	mingw32-x-sdl mingw32-x-libvorbis mingw32-x-fluidsynth mingw32-x-stk
 	mingw32-x-glib2 mingw32-x-portaudio mingw32-x-libsndfile mingw32-x-fftw
 	mingw32-x-flac mingw32-x-fltk mingw32-x-libsamplerate

data/locale/CMakeLists.txt

@@ -3,6 +3,17 @@ if (QT5)
 	set (QT_LRELEASE_EXECUTABLE "${Qt5_LRELEASE_EXECUTABLE}")
 endif ()
 
+IF(QT_LUPDATE_EXECUTABLE STREQUAL "")
+	EXECUTE_PROCESS(COMMAND "lupdate" "--help" RESULT_VARIABLE LUPDATE_FALLBACK OUTPUT_QUIET)	
+	IF(LUPDATE_FALLBACK EQUAL 0)
+        	SET(QT_LUPDATE_EXECUTABLE lupdate)
+        	SET(QT_LRELEASE_EXECUTABLE lrelease)
+	ELSE()
+		MESSAGE(FATAL_ERROR "Cannot generate locales")
+	ENDIF()
+ENDIF()
+
+
 #
 # rules for building localizations
 #