meta: Enable clang as default native compiler

meta: Enable clang as default native compiler

Fix few packages which do not yet build with clang
There is one issue to tackle, when using clang for cross compiler
it also installs native clang which is then picked by the build system
if a package's build system has pieces to build for native build host
There are only handful of such packages but there are few e.g.
gmp, nettle which check for CC_FOR_BUILD during configure and it ends
up using clang from own build and does not find right libraries in
native sysroot, maybe we should add libcxx-native and compiler-rt-native
to DEFAULT_DEPENDENCIES list when llvm runtime is used.

gobject-introspection uses gcc for native builds

Its fails when built with clang

FileNotFoundError: [Errno 2] No such file or directory: 'ldd'
...

| FAILED: [code=1] gir/GLib-2.0.gir

Signed-off-by: Khem Raj <raj.khem@gmail.com>