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

libc/linux/munmap.h

@@ -3,12 +3,26 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 
 forceinline long LinuxMunmap(void *addr, size_t size) {
+#ifdef __x86_64__
   long rc;
   asm volatile("syscall"
                : "=a"(rc)
                : "0"(0xb), "D"(addr), "S"(size)
                : "rcx", "r11", "memory");
   return rc;
+#elif defined(__aarch64__)
+  register long r0 asm("x0") = (long)addr;
+  register long r1 asm("x1") = (long)size;
+  register long res_x0 asm("x0");
+  asm volatile("mov\tx8,%1\n\t"
+               "svc\t0"
+               : "=r"(res_x0)
+               : "i"(215), "r"(r0), "r"(r1)
+               : "x8", "memory");
+  return res_x0;
+#else
+#error "unsupported architecture"
+#endif
 }
 
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */