Merge pull request #765 from Susurrus/qt5_win_fixes

Documenting why unit tests are in release build.

qgroundcontrol.pro

@@ -750,10 +750,8 @@ SOURCES += \
 
 #
 # Unit Test specific configuration goes here
-#
-# FIXME: These files should only be enabled on the Debug build, but that is currently broken as of Qt5.3.1 on Windows,
-#        so we just always compile them.
-#ReleaseBuild {
+# We'd ideally only build this code as part of a Debug build, but qmake doesn't allow
+# for Debug-only files when generating Visual Studio projects [QTBUG-40351]
 INCLUDEPATH += \
 	src/qgcunittest
 
@@ -784,4 +782,3 @@ SOURCES += \
 	src/qgcunittest/TCPLinkTest.cc \
 	src/qgcunittest/TCPLoopBackServer.cc \
 	src/qgcunittest/QGCUASFileManagerTest.cc
-#}