Revert "runtime: don't forward SIGPIPE on macOS"

This reverts CL 188297.

Reason for revert: broke multiple of the darwin builders.

Fixes #33943.

Change-Id: Iacff98d1450edc70402dc7a220d16fcd73337c9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/191784
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

misc/cgo/testcarchive/testdata/main3.c

@@ -12,7 +12,6 @@
 #include <time.h>
 #include <sched.h>
 #include <unistd.h>
-#include <pthread.h>
 
 #include "libgo3.h"
 
@@ -52,18 +51,11 @@ static void init() {
 	}
 }
 
-static void *provokeSIGPIPE(void *arg) {
-	ProvokeSIGPIPE();
-	return NULL;
-}
-
 int main(int argc, char** argv) {
 	int verbose;
 	struct sigaction sa;
 	int i;
 	struct timespec ts;
-	int res;
-	pthread_t tid;
 
 	verbose = argc > 2;
 	setvbuf(stdout, NULL, _IONBF, 0);
@@ -76,19 +68,6 @@ int main(int argc, char** argv) {
 	// a non-default SIGPIPE handler before the runtime initializes.
 	ProvokeSIGPIPE();
 
-	// Test that SIGPIPE on a non-main thread is also handled by Go.
-	res = pthread_create(&tid, NULL, provokeSIGPIPE, NULL);
-	if (res != 0) {
-		fprintf(stderr, "pthread_create: %s\n", strerror(res));
-		exit(EXIT_FAILURE);
-	}
-
-	res = pthread_join(tid, NULL);
-	if (res != 0) {
-		fprintf(stderr, "pthread_join: %s\n", strerror(res));
-		exit(EXIT_FAILURE);
-	}
-
 	if (verbose) {
 		printf("calling sigaction\n");
 	}

src/runtime/signal_unix.go

@@ -636,13 +636,6 @@ func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
 		return true
 	}
 
-	// This function and its caller sigtrampgo assumes SIGPIPE is delivered on the
-	// originating thread. This property does not hold on macOS (golang.org/issue/33384),
-	// so we have no choice but to ignore SIGPIPE.
-	if GOOS == "darwin" && sig == _SIGPIPE {
-		return true
-	}
-
 	// If there is no handler to forward to, no need to forward.
 	if fwdFn == _SIG_DFL {
 		return false