Bug#854159: gcc-6: disable libmpx in stage1 and stage2 builds

[Helmut Grohne <helmut@subdivi.de>]

Source: gcc-6
Tags: patch
User: helmutg@debian.org
Usertags: rebootstrap

It was never possible to bootstrapp x86 architectures using gcc-6,
because stage1 and stage2 compilers were never buildable. That's due to
gcc-6 enabling libmpx by default. However, libmpx needs a working libc.
Thus the staged builds should disable libmpx (like they are disabling
libatomic, libgomp and libssp). Please consider applying the attached
patch

Helmut

--- a/debian/rules2
+++ b/debian/rules2
@@ -221,6 +221,7 @@
 	--disable-decimal-float \
 	--disable-libatomic  \
 	--disable-libgomp  \
+	--disable-libmpx \
 	--disable-libssp \
 	--disable-libquadmath \
 	--disable-libsanitizer \