Usually I do weekly builds of GCC snapshots on Cygwin, but current snapshot (http://gcc.gnu.org/ml/gcc/2013-04/msg00091.html) fails with:
... g++ -c -DIN_GCC_FRONTEND -DIN_GCC_FRONTEND -g -DIN_GCC -fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wwrite-strings -Wcast-qual -DHAVE_CONFIG_H -I. -Ic-family -I/home/pippo/gcc/gcc-4.9-20130407/gcc -I/home/pippo/gcc/gcc-4.9-20130407/gcc/c-family -I/home/pippo/gcc/gcc-4.9-20130407/gcc/../include -I/home/pippo/gcc/gcc-4.9-20130407/gcc/../libcpp/include -I/home/pippo/gcc/gcc-4.9-20130407/gcc/../libdecnumber -I/home/pippo/gcc/gcc-4.9-20130407/gcc/../libdecnumber/bid -I../libdecnumber -I/home/pippo/gcc/gcc-4.9-20130407/gcc/../libbacktrace /home/pippo/gcc/gcc-4.9-20130407/gcc/c-family/c-dump.c -o c-family/c-dump.o /home/pippo/gcc/gcc-4.9-20130407/gcc/c-family/c-cppbuiltin.c: In function ‘void c_cpp_builtins(cpp_reader*)’: /home/pippo/gcc/gcc-4.9-20130407/gcc/c-family/c-cppbuiltin.c:914:3: error: ‘TARGET_CYGWIN64’ was not declared in this scope ... I am building on an AMD Athlon 64 2C with XP 32 an Cygwin 1.7.17 (the official 32b distribution). Ciao, Angelo.