bitbake: Fix for pthreads C test w/yocto

Fixed a problem where the C/CXX compile flags were getting
overwritten.  Fixed warnings in a few sensor drivers.

This commit fixes #485

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/htu21d/htu21d.cpp

@@ -202,7 +202,7 @@ HTU21D::testSensor(void)
     int iError = 0;
     float fTemp, fHum;
     float fTempMax, fTempMin;
-    float fHumMax, fHumMin;
+    float fHumMax = 0.0, fHumMin = 0.0;
     float fTempFirst;
 
     fprintf(stdout, "Executing Sensor Test\n" );