kbuild: clang: add -no-integrated-as to KBUILD_[AC]FLAGS

commit a37c45cd82e62a361706b9688a984a3a63957321 upstream.

The Linux Kernel relies on GCC's acceptance of inline assembly as an
opaque object which will not have any validation performed on the content.
The current behaviour in LLVM is to perform validation of the contents by
means of parsing the input if the MC layer can handle it.

Disable clangs integrated assembler and use the GNU assembler instead.

Wording-mostly-from: Saleem Abdulrasool <compnerd@compnerd.org>
Signed-off-by: Michael Davidson <md@google.com>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>