Add a "fork" of musl as //fusl.

fusl/src/signal/block.c

+#include "pthread_impl.h"
+#include "syscall.h"
+#include <signal.h>
+
+static const unsigned long all_mask[] = {
+#if ULONG_MAX == 0xffffffff && _NSIG == 129
+        -1UL, -1UL, -1UL, -1UL
+#elif ULONG_MAX == 0xffffffff
+        -1UL, -1UL
+#else
+        -1UL
+#endif
+};
+
+static const unsigned long app_mask[] = {
+#if ULONG_MAX == 0xffffffff
+#if _NSIG == 65
+        0x7fffffff, 0xfffffffc
+#else
+        0x7fffffff, 0xfffffffc, -1UL, -1UL
+#endif
+#else
+#if _NSIG == 65
+        0xfffffffc7fffffff
+#else
+        0xfffffffc7fffffff, -1UL
+#endif
+#endif
+};
+
+void __block_all_sigs(void *set)
+{
+        __syscall(SYS_rt_sigprocmask, SIG_BLOCK, &all_mask, set, _NSIG/8);
+}
+
+void __block_app_sigs(void *set)
+{
+        __syscall(SYS_rt_sigprocmask, SIG_BLOCK, &app_mask, set, _NSIG/8);
+}
+
+void __restore_sigs(void *set)
+{
+        __syscall(SYS_rt_sigprocmask, SIG_SETMASK, set, 0, _NSIG/8);
+}