toolchain/52797: Conflicting implementation of asnprintf() in Cygwin

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>Number:         52797
>Category:       toolchain
>Synopsis:       Conflicting implementation of asnprintf() in Cygwin
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 09 03:15:00 +0000 2017
>Originator:     Sevan Janiyan
>Release:        NetBSD-8 & -current
>Organization:
>Environment:
CYGWIN_NT-6.1 X61s 2.9.0(0.318/5/3) 2017-09-12 10:18 x86_64 Cygwin
>Description:
Attempting to cross build the tools on Cygwin fails due to the following error:
#   compile  compat/atoll.lo
cc -O  -I. -I./include -I/cygdrive/c/Users/Me/Downloads/src/tools/compat -I/cygdrive/c/Users/Me/Downloads/src/tools/compat/sys  -DHAVE_NBTOOL_CONFIG_H=1 -D_FILE_OFFSET_BITS=64 -D__DBINTERFACE_PRIVATE -c -o atoll.lo.o    /cygdrive/c/Users/Me/Downloads/src/lib/libc/stdlib/atoll.c
In file included from ./nbtool_config.h:867:0,
                 from /cygdrive/c/Users/Me/Downloads/src/lib/libc/stdlib/atoll.c:33:
/cygdrive/c/Users/Me/Downloads/src/tools/compat/compat_defs.h:238:5: error: conflicting types for 'asnprintf'
 int asnprintf(char **, size_t, const char *, ...);
     ^~~~~~~~~
In file included from /usr/include/sys/types.h:20:0,
                 from /cygdrive/c/Users/Me/Downloads/src/tools/compat/compat_defs.h:35,
                 from ./nbtool_config.h:867,
                 from /cygdrive/c/Users/Me/Downloads/src/lib/libc/stdlib/atoll.c:33:
/usr/include/stdio.h:288:8: note: previous declaration of 'asnprintf' was here
 char * _EXFUN(asnprintf, (char *__restrict, size_t *__restrict, const char *__restrict, ...)
        ^

*** Failed target:  atoll.lo

Using GCC 6.4 from Cygwin
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-cygwin/6.4.0/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with: /cygdrive/i/szsz/tmpp/gcc/gcc-6.4.0-4.x86_64/src/gcc-6.4.0/configure --srcdir=/cygdrive/i/szsz/tmpp/gcc/gcc-6.4.0-4.x86_64/src/gcc-6.4.0 --prefix=/usr --exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc --docdir=/usr/share/doc/gcc --htmldir=/usr/share/doc/gcc/html -C --build=x86_64-pc-cygwin --host=x86_64-pc-cygwin --target=x86_64-pc-cygwin --without-libiconv-prefix --without-libintl-prefix --libexecdir=/usr/lib --enable-shared --enable-shared-libgcc --enable-static --enable-version-specific-runtime-libs --enable-bootstrap --enable-__cxa_atexit --with-dwarf2 --with-tune=generic --enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-graphite --enable-threads=posix --enable-libatomic --enable-libcilkrts --enable-libgomp --enable-libitm --enable-libquadmath --enable-libquadmath-support --enable-libssp --enable-libada --disable-symvers --with-gnu-ld --with-gnu-as --with-cloog-include=/usr/include/cloog-isl --without-libiconv-prefix --without-libintl-prefix 
 --with-system-zlib --enable-linker-build-id --with-default-libstdcxx-abi=gcc4-compatible
Thread model: posix
gcc version 6.4.0 (GCC)

>How-To-Repeat:
Attempting to build the toolchain on Cygwin
./build.sh -U -m amd64 tools kernel=GENERIC
>Fix: