There are some people interested in experimenting with Clang's
integrated assembler. To make it easy to do so without source
modification, allow the user to specify 'AS=clang' as part of the
make command to avoid adding '-no-integrated-as' to the {A,C}FLAGS.

Link: https://github.com/ClangBuiltLinux/linux/issues/577Suggested-by: NDmitry Golovin <dima@golovin.in>
Signed-off-by: NNathan Chancellor <natechancellor@gmail.com>
Reviewed-by: NNick Desaulniers <ndesaulniers@google.com>
Tested-by: NNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>