[refs: http://gcc.gnu.org/ml/gcc/2009-01/threads.html#00060
       http://gcc.gnu.org/ml/gcc/2009-01/threads.html#00216 ]

Bootstrap on cygwin is currently failing during stage 3 with:

	  /home/andy/live-gcc/my_gcc/./gcc/xgcc
-B/home/andy/live-gcc/my_gcc/./gcc/ -B/usr/local/i686-pc-cygwin/bin/
-B/usr/local/i686-pc-cygwin/lib/ -isystem
/usr/local/i686-pc-cygwin/include -isystem
/usr/local/i686-pc-cygwin/sys-include -c -DHAVE_CONFIG_H -g -O2    -I.
-I../../../gcc/libiberty/../include  -W -Wall -Wwrite-strings
-Wc++-compat -Wstrict-prototypes -pedantic
../../../gcc/libiberty/strsignal.c -o pic/strsignal.o; \
	else true; fi
/home/andy/live-gcc/my_gcc/./gcc/xgcc
-B/home/andy/live-gcc/my_gcc/./gcc/ -B/usr/local/i686-pc-cygwin/bin/
-B/usr/local/i686-pc-cygwin/lib/ -isystem
/usr/local/i686-pc-cygwin/include -isystem
/usr/local/i686-pc-cygwin/sys-include -c -DHAVE_CONFIG_H -g -O2    -I.
-I../../../gcc/libiberty/../include  -W -Wall -Wwrite-strings
-Wc++-compat -Wstrict-prototypes -pedantic
../../../gcc/libiberty/strsignal.c -o strsignal.o
../../../gcc/libiberty/strsignal.c:408: error: conflicting types for 'strsignal'
/usr/include/string.h:78: note: previous declaration of 'strsignal' was here
make[2]: *** [strsignal.o] Error 1
make[2]: Leaving directory `/home/andy/live-gcc/my_gcc/i686-pc-cygwin/libiberty'
make[1]: *** [all-target-libiberty] Error 2
make[1]: Leaving directory `/home/andy/live-gcc/my_gcc'
make: *** [all] Error 2

This happens because libiberty configure has a hard-coded hack that kicks in when building libiberty as a target library, which causes strsignal (and a couple of others) to be removed from the list of functions for configure to check against the system libraries, causing the libiberty versions to be built when they aren't needed.  (They used to be required; formerly, Cygwin pulled in the object files from libiberty when linking the DLL, but this was fixed some time ago and the hack has been obsolete since then).  I am testing a patch to remove the hack.