I've observed a make race when building in parallel against 3.1.1 and 3.1.2.

Reproducibility is low - I've had a CI machine building ~once a week for over a year and just now its hit twice in a row - never before.  Can't reproduce it on my own machine.

> $ git clone ...
> ./configure --prefix=/path/to/sysroot/rpi/usr --disable-ipv6 --disable-locale --disable-iconv-open --disable-iconv --disable-acl-support --disable-xattr-support --host=arm-linux-gnueabihf
> $ make -j8
> perl ./mkproto.pl ./*.c ./lib/compat.c
> sed 's;\@bindir\@;/home/buildbot/slaves/enterprise-master/enterprise-rootfs-master/build/sysroot/rpi/usr/bin;g' <./rsync-ssl.in >rsync-ssl
> sed 's;\@stunnel4\@;stunnel;g' <./stunnel-rsync.in >stunnel-rsync
> sed 's;\@bindir\@;/home/buildbot/slaves/enterprise-master/enterprise-rootfs-master/build/sysroot/rpi/usr/bin;g' <./stunnel-rsyncd.conf.in >stunnel-rsyncd.conf
> Copying srcdir rsync.1
> cp: cannot stat ‘./rsync.1’: No such file or directory
> make: [man-copy] Error 1 (ignored)
> Copying srcdir rsyncd.conf.5
> cp: cannot stat ‘./rsyncd.conf.5’: No such file or directory
> make: [man-copy] Error 1 (ignored)
> arm-linux-gnueabihf-gcc -std=gnu99 -I. -I. -I./zlib -I./popt -g -O2 -DHAVE_CONFIG_H -Wall -W -Wno-unused-parameter  -c rsync.c -o rsync.o
> In file included from ./rounding.c:20:0:
> ./rsync.h:1006:19: fatal error: proto.h: No such file or directory
>  #include "proto.h"
>                    ^
> compilation terminated.
> Failed to create rounding.h!
> make: *** [rounding.h] Error 1
> make: *** Waiting for unfinished jobs....