Because of the gcc-crosssdk bug, cmake-nativesdk needs to search gcc
standard paths itself. Right now it was fixed, so remove the additional
CXXFLAG for cmake-nativesdk.
(From OE-Core rev: bac15cc98e136892d4c09f2470622965bd9dbbeb)
Signed-off-by: Kang Kai <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>