Mark qtlocation as warning-free

This will turn -Werror on for our tested compilers, to avoid introducing
new warnings.

Change-Id: I27b55fdf514247549455fffd14b17ae6dce9976f
Reviewed-by: Paolo Angelelli <paolo.angelelli@qt.io>
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

.qmake.conf

 load(qt_build_config)
 
+CONFIG += warning_clean
 MODULE_VERSION = 5.9.0

src/location/location.pro

@@ -7,6 +7,9 @@ android {
 
 CONFIG += simd optimize_full
 
+# 3rdparty headers produce warnings with MSVC
+msvc: CONFIG -= warning_clean
+
 INCLUDEPATH += ../3rdparty/poly2tri
 INCLUDEPATH += ../3rdparty/clipper
 INCLUDEPATH += ../3rdparty/clip2tri