llvm: remove LLVM_LDFLAGS from llvm-config --ldflags output

llvm: remove LLVM_LDFLAGS from llvm-config --ldflags output

On native OE builds the LLVM_LDFLAGS gets a lot of extra flags which may
depend on exact build dir and as such be inappropriate to binaries
shared through sstate-cache. It is not possible to override this
behaviour in llvm-config since crossscripts are not being used for
native builds. Ignore LLVM_LDFLAGS for native builds.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>