tools: Remove some options from CLANG_CROSS_FLAGS

These options are not needed with OE/Yocto since compiler is already
passing these options via TOOLCHAIN_OPTIONS, having these options infact
regressed OE builds because build time --sysroot on OE cross compiler is
/not/exist and that creates problems where clang can no more find system
headers anymore during compilation

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>