win32: emulate SIGPIPE

The code to check whether a write error is due to a broken pipe
can now either:

- return with error EPIPE;
- cause the process to exit with code 128+SIGPIPE.

The default is the latter but the behaviour can be changed by issuing
signal(SIGPIPE, SIG_IGN) and signal(SIGPIPE, SIG_DFL) calls.

No actual signal is involved so kill can't send SIGPIPE and handlers
other than SIG_IGN and SIG_DFL aren't supported.

This does, however, avoid unsightly 'broken pipe' errors from commands
like the example in GitHub issue #99:

  dd if=/dev/urandom | tr -dc _A-Z-a-z-0-9 | head -c${1:-32};echo;

2 files changed, 4 insertions, 2 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 4ac749fd3..a17da9c1f 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -536,9 +536,7 @@ enum {
 #endif
                 + (1LL << SIGINT)
                 + (1LL << SIGTERM)
-#ifdef SIGPIPE
                 + (1LL << SIGPIPE)   // Write to pipe with no readers
-#endif
 #ifdef SIGQUIT
                 + (1LL << SIGQUIT)   // Quit from keyboard
 #endif
diff --git a/include/mingw.h b/include/mingw.h
index a1869227d..8a695d2d2 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -93,10 +93,14 @@ IMPL(getpwent,struct passwd *,NULL,void)
  * signal.h
  */
 #define SIGKILL 9
+#define SIGPIPE 13
 
 #define SIG_UNBLOCK 1
 
 NOIMPL(FAST_FUNC sigprocmask_allsigs, int how UNUSED_PARAM);
+typedef void (*sighandler_t)(int);
+sighandler_t winansi_signal(int signum, sighandler_t handler);
+#define signal(s, h) winansi_signal(s, h)
 
 /*
  * stdio.h