Port a lot more code to AARCH64

- Introduce epoll_pwait()
- Rewrite -ftrapv and ffs() libraries in C code
- Use more FreeBSD code in math function library
- Get significantly more tests passing on qemu-aarch64
- Fix many Musl long double functions that were broken on AARCH64

test/libc/runtime/sigsetjmp_test.c

@@ -25,6 +25,7 @@
 #include "libc/sysv/consts/sa.h"
 #include "libc/sysv/consts/sig.h"
 #include "libc/testlib/testlib.h"
+#ifdef __x86_64__
 
 sigjmp_buf jb;
 volatile int sigs;
@@ -54,3 +55,5 @@ TEST(sigsetjmp, test) {
   ASSERT_EQ(1000, jumps);
   ASSERT_EQ(1000, sigs);
 }
+
+#endif /* __x86_64__ */