nss: Fix build with clang

nss: Fix build with clang

Add a patch to disable a clang specific warning
and avoid passing clang options to gcc when we have
cross compiler is clang but host compiler is gcc
We do not need to use target cflags when building
native pieces and hence avoid the inter-mixing of
compiler options

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>