RTEMS 4.11.0 build fails on Windows

[Linda Huxley]

I am attempting to build the RTEMS tool set, following the instructions 
in section "5.2.1. RTEMS Tools and Kernel" of the "RTEMS User Manual" 
4.11.99.  The instructions for building on Windows are flawed, but I 
seem to have worked my way through the issues.  I am working in the 
MSYS2 MINGW64 build environment.  I issue the following commands:

$ cd /c
$ mkdir -p opt/rtems
$ cd opt/rtems
$ wget 
https://ftp.rtems.org/pub/rtems/releases/4.11/4.11.0/rtems-source-builder-4.11.0.tar.xz
$ tar Jxf rtems-source-builder-4.11.0.tar.xz
$ mv rtems-source-builder-4.11.0 4.11.0
$ cd 4.11.0/rtems
$ ../source-builder/sb-set-builder \
     --prefix=/opt/rtems/4.11.0 4.11/rtems-sparc --jobs=none

About 45 minutes later, the build fails with the following message:

error: building srg4n2xwm1
Build FAILED
   See error report: 
rsb-report-sparc-rtems4.11-gcc-4.9.3-newlib-2.2.0.20150423-x86_64-w64-mingw32-1.txt
error: building srg4n2xwm1
Build Set: Time 0:40:06.527128
Build FAILED

The salient error messages at the bottom of error report would appear to be:

In file included from ../../gcc-4.9.3/gcc/cp/except.c:1013:0:
cfns.gperf: In function 'const char* libc_name_p(const char*, unsigned 
int)':
cfns.gperf:101:1: error: 'const char* libc_name_p(const char*, unsigned 
int)' redeclared inline with 'gnu_inline' attribute
cfns.gperf:26:14: note: 'const char* libc_name_p(const char*, unsigned 
int)' previously declared here
cfns.gperf: At global scope:
cfns.gperf:26:14: warning: inline function 'const char* 
libc_name_p(const char*, unsigned int)' used but never defined
make[2]: *** [Makefile:1058: cp/except.o] Error 1
make[2]: Leaving directory 
'/C/opt/rtems/4.11.0/rtems/build/srg4n2xwm1/build/gcc'
make[1]: *** [Makefile:3985: all-gcc] Error 2
make[1]: Leaving directory 
'/C/opt/rtems/4.11.0/rtems/build/srg4n2xwm1/build'
make: *** [Makefile:872: all] Error 2
shell cmd failed: sh -ex  /C/opt/rtems/4.11.0/rtems/build/srg4n2xwm1/doit
error: building srg4n2xwm1

This would appear to be a bug in gcc itself.  I tried making the obvious 
changes to cfns.h, but the file is overwritten when I restart RSB.

Can anybody provide a clue as to how to resolve this error?  Has anybody 
successfully built RTEMS 4.11.0 recently?