[eclipse-poky] eclipse-poky using host gcc/g++ for indexing

[Ang, Chin Huat]

It appears that when eclipse-cdt tries to look for header files it failed to pick up gcc from SDK and instead uses host distro's gcc, thus showing header files from the host instead of SDK.

I've experimented manually workaround the indexer settings by changing the gcc dump spec command from ${COMMAND} to ${CC} as the indexer appears to support using environment variables as fallback, and I see the SDK header files being discovered correctly. 

Next I will look into how to programmatically update C/C++ indexer command by language setting provider API in YoctoSDK*ProjectNature, although I am slightly concerned about customizing the default indexer command.  

https://bugzilla.yoctoproject.org/show_bug.cgi?id=12431

--Chin Huat