Ian, 

A recent changes of tools evtchn cause a build failure with gcc 4.4.7, OS is RHEL6.5.

Bad commit:
commit b7f76a699dcfadc0a52ab45b33cc72dbf3a69e7b
Author: Ian Campbell <ian.campbell@citrix.com>
Date:   Mon Jun 1 16:20:09 2015 +0100

    tools: Refactor /dev/xen/evtchn wrappers into libxenevtchn.

    libxenevtchn will provide a stable API and ABI for accessing the
¡¡evtchn device.


Partial error log:
...
gcc  -DPIC -O1 -fno-omit-frame-pointer -m64 -g -fno-strict-aliasing -std=gnu99 -Wall -Wstrict-prototypes -Wdeclaration-after-statement -Wno-unused-but-set-variable   -O0 -g3 -D__XEN_TOOLS__ -MMD -MF .linux.opic.d -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -fno-optimize-sibling-calls  -Werror -Wmissing-prototypes -I./include -I/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/include -I/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/libs/toollog/include -I/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/include  -fPIC -c -o linux.opic linux.c 
mv headers.chk.new headers.chk
In file included from private.h:5,
                 from core.c:19:
./include/xenevtchn.h:36: error: redefinition of typedef ¡®xentoollog_logger¡¯
/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/libs/toollog/include/xentoollog.h:44: note: previous declaration of ¡®xentoollog_logger¡¯ was here
In file included from private.h:5,
                 from core.c:19:
./include/xenevtchn.h:36: error: redefinition of typedef ¡®xentoollog_logger¡¯
/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/libs/toollog/include/xentoollog.h:44: note: previous declaration of ¡®xentoollog_logger¡¯ was here
make[6]: *** [core.opic] Error 1
make[6]: *** Waiting for unfinished jobs....
make[6]: *** [core.o] Error 1
In file included from private.h:5,
                 from linux.c:29:
./include/xenevtchn.h:36: error: redefinition of typedef ¡®xentoollog_logger¡¯
/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/libs/toollog/include/xentoollog.h:44: note: previous declaration of ¡®xentoollog_logger¡¯ was here
In file included from private.h:5,
                 from linux.c:29:
./include/xenevtchn.h:36: error: redefinition of typedef ¡®xentoollog_logger¡¯
/home/www/builds_xen_unstable/xen-src-2e46e3f2-20160127/tools/libs/evtchn/../../../tools/libs/toollog/include/xentoollog.h:44: note: previous declaration of ¡®xentoollog_logger¡¯ was here
make[6]: *** [linux.o] Error 1
make[6]: *** [linux.opic] Error 1
...

¡¡
Best Regards,
Xudong