Commit 0c3b7e42 ("tools build: Add support for host programs format")
introduced host_c_flags which referenced CHOSTFLAGS. The actual name of the
variable is HOSTCFLAGS. Fix this up.

Fixes: 0c3b7e42 ("tools build: Add support for host programs format")
Signed-off-by: NLaura Abbott <labbott@redhat.com>
Acked-by: NJiri Olsa <jolsa@kernel.org>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>