1.20_linux: remove signal.h usages

Closes #24

1.20_linux/runtime/cgo/gcc_linux_amd64.c.patch

@@ -0,0 +1,59 @@
+//--from
+#include <pthread.h>
+#include <errno.h>
+#include <string.h> // strerror
+#include <signal.h>
+#include <stdlib.h>
+#include "libcgo.h"
+#include "libcgo_unix.h"
+//--to
+#include <pthread.h>
+#include <errno.h>
+#include <string.h> // strerror
+#include <stdlib.h>
+#include "libcgo.h"
+#include "libcgo_unix.h"
+//--from
+void
+_cgo_sys_thread_start(ThreadStart *ts)
+{
+	pthread_attr_t attr;
+	sigset_t ign, oset;
+	pthread_t p;
+	size_t size;
+	int err;
+
+	sigfillset(&ign);
+	pthread_sigmask(SIG_SETMASK, &ign, &oset);
+
+	pthread_attr_init(&attr);
+	pthread_attr_getstacksize(&attr, &size);
+	// Leave stacklo=0 and set stackhi=size; mstart will do the rest.
+	ts->g->stackhi = size;
+	err = _cgo_try_pthread_create(&p, &attr, threadentry, ts);
+
+	pthread_sigmask(SIG_SETMASK, &oset, nil);
+
+	if (err != 0) {
+		fatalf("pthread_create failed: %s", strerror(err));
+	}
+}
+//--to
+void
+_cgo_sys_thread_start(ThreadStart *ts)
+{
+	pthread_attr_t attr;
+	pthread_t p;
+	size_t size;
+	int err;
+
+	pthread_attr_init(&attr);
+	pthread_attr_getstacksize(&attr, &size);
+	// Leave stacklo=0 and set stackhi=size; mstart will do the rest.
+	ts->g->stackhi = size;
+	err = _cgo_try_pthread_create(&p, &attr, threadentry, ts);
+
+	if (err != 0) {
+		fatalf("pthread_create failed: %s", strerror(err));
+	}
+}