bootstrap-fix-include-next

bootstrap-fix-include-next

When doing a bootstrap, we use a newly built clang.
When this one is used, if already installed on the system,
we have clang header in two places:
llvm-toolchain-7-7/build-llvm/lib/clang/7.0.0/include/inttypes.h
and
/usr/include/clang/7.0.0/include/inttypes.h

Because clang expects only one of his headers to be available, it uses
include_next to get the glibc (libc6-dev package) header.

However, in the previous example, because we have inttypes.h twice in the
include search path, clang's header will call itself without any effect.
Therefor, it will do include_next until the define from the libc is existing (ex: _INTTYPES_H)

Gbp-Pq: Name bootstrap-fix-include-next.diff