Building cross x86_64-unknown-linux-gnu to i686-pc-cygwin:

libtool: compile:  /SCRATCH/tmp.uPE4kUseBu/gcc-4.5.3/gcc-4.5.3/./gcc/xgcc -shared-libgcc -B/SCRATCH/tmp.uPE4kUseBu/gcc-4.5.3/gcc-4.5.3/./gcc -nostdinc++ -L/SCRATCH/tmp.uPE4kUseBu/gcc-4.5.3/gcc-4.5.3/i686-pc-cygwin/libstdc++-v3/src -L/SCRATCH/tmp.uPE4kUseBu/gcc-4.5.3/gcc-4.5.3/i686-pc-cygwin/libstdc++-v3/src/.libs -B/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/bin/ -B/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/lib/ -isystem /opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/include -isystem /opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/sys-include -DHAVE_CONFIG_H -I. -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava -I./include -I./gcj -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava -Iinclude -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/include -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/classpath/include -Iclasspath/include -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/classpath/native/fdlibm -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/../boehm-gc/include -I../boehm-gc/include -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/.././libjava/../gcc -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/../zlib -I/opt/devel/gnu/src/gcc-cygwin/gcc-4.5.3/libjava/../libffi/include -I../libffi/include -fno-rtti -fnon-call-exceptions -fdollars-in-identifiers -Wswitch-enum -D_FILE_OFFSET_BITS=64 -ffloat-store -fomit-frame-pointer -Usun -Wextra -Wall -D_GNU_SOURCE -DPREFIX=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3\" -DTOOLEXECLIBDIR=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/lib\" -DJAVA_HOME=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3\" -DBOOT_CLASS_PATH=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/share/java/libgcj-4.5.3.jar\" -DJAVA_EXT_DIRS=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/share/java/ext\" -DGCJ_ENDORSED_DIRS=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/share/java/gcj-endorsed\" -DGCJ_VERSIONED_LIBDIR=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/lib/gcj-4.5.3-11\" -DPATH_SEPARATOR=\":\" -DECJ_JAR_FILE=\"\" -DLIBGCJ_DEFAULT_DATABASE=\"/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/lib/gcj-4.5.3-11/classmap.db\" -DLIBGCJ_DEFAULT_DATABASE_PATH_TAIL=\"gcj-4.5.3-11/classmap.db\" -g -O2 -MT java/net/natVMInetAddress.lo -MD -MP -MF java/net/.deps/natVMInetAddress.Tpo -c java/net/natVMInetAddress.cc  -DDLL_EXPORT -DPIC -o java/net/.libs/natVMInetAddress.o

java/net/natVMInetAddress.cc:42:52: error: declaration of C function ‘int gethostname(char*, int)’ conflicts with
/opt/devel/gnu/cross-gcc/Linux/x86_64-unknown-linux-gnu/openSUSE_11.3/cross/CYGWIN_NT-5.1/i686-pc-cygwin/cygwin-1.7.9-1/gcc-4.5.3/i686-pc-cygwin/include/sys/unistd.h:232:6: error: previous declaration ‘int gethostname(char*, size_t)’ here

It seems somehow related to PR45872.


java/net/natVMInetAddressPosix.cc has:
#ifndef HAVE_GETHOSTNAME_DECL
extern "C" int gethostname (char *name, int namelen);
#endif

But HAVE_GETHOSTNAME_DECL isn't defined.
A grep in the libjava build tree gives:
include/config.h:/* #undef HAVE_GETHOSTNAME_DECL */
java/net/natVMInetAddress.cc:#ifndef HAVE_GETHOSTNAME_DECL

I don't know if it's cause by the fact that cygwin has it's unistd.h in the include/sys directory, not in include.