compiler, clang: properly override 'inline' for clang

Commit abb2ea7d

 ("compiler, clang: suppress warning for unused
static inline functions") just caused more warnings due to re-defining
the 'inline' macro.

So undef it before re-defining it, and also add the 'notrace' attribute
like the gcc version that this is overriding does.

Maybe this makes clang happier.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>