build env:
building on Ubuntu 18.04.5 LTS to QNX 7.1.0 (SDP toolchain)
Poco 1.13.3

Error:
I'm trying to build Poco 1.13.3, but getting the following error:
poco-1.13.3-all/Net/src/SocketImpl.cpp: In member function 'Poco::Int64 Poco::Net::SocketImpl::sendFile(Poco::FileInputStream&, Poco::UInt64)':
poco-1.13.3-all/Net/src/SocketImpl.cpp:1443:2: error: 'sighandler_t' was not declared in this scope
sighandler_t sigPrev = signal(SIGPIPE, SIG_IGN);
^~~~~~~~~~~~
poco-1.13.3-all/Net/src/SocketImpl.cpp:1443:2: note: suggested alternative: 'sa_handler'
sighandler_t sigPrev = signal(SIGPIPE, SIG_IGN);
^~~~~~~~~~~~
sa_handler
poco-1.13.3-all/Net/src/SocketImpl.cpp:1449:18: error: 'sigPrev' was not declared in this scope
signal(SIGPIPE, sigPrev != SIG_ERR ? sigPrev : SIG_DFL);
^~~~~~~
poco-1.13.3-all/Net/src/SocketImpl.cpp:1449:18: note: suggested alternative: 'strrev'
signal(SIGPIPE, sigPrev != SIG_ERR ? sigPrev : SIG_DFL);

Reason and proposed solution:
from signal(2) — Linux manual page:
The use of sighandler_t is a GNU extension, exposed if
_GNU_SOURCE is defined

I've tried to pass the flag ' -D_GNU_SOURCE' to C and C++ flags, and in toolchain.cmake, but it didn't work.
also tried to define it in poco-1.13.3-all/Net/src/SocketImpl.cpp:
#define _GNU_SOURCE

but it didn't solve the error.

the only thing that helped was to define sigPrev as void (*sigPrev)(int); (which is the definition of sighandler_t).
method after fix:
Poco::Int64 SocketImpl::sendFile(FileInputStream &fileInputStream, Poco::UInt64 offset)
{
FileIOS::NativeHandle fd = fileInputStream.nativeHandle();
Poco::UInt64 fileSize = fileInputStream.size();
std::streamoff sentSize = fileSize - offset;
Poco::Int64 sent = 0;
void (*sigPrev)(int);
sigPrev = signal(SIGPIPE, SIG_IGN);
while (sent == 0)
{
errno = 0;
sent = _sendfile(_sockfd, fd, offset, sentSize);
}
signal(SIGPIPE, sigPrev != SIG_ERR ? sigPrev : SIG_DFL);
return sent;
}

with this change, Poco compiled successfully.

it is also mentioned in the man file that:
"WARNING: the behavior of signal() varies across UNIX versions,
and has also varied historically across different versions of
Linux. Avoid its use: use sigaction(2) instead. See Portability
below."
so, maybe it is worth considering switching to sigaction.

bottom line:
can you add the fix or suggest a better approach?

Thanks,
Michael