linux: make write syscall available

The jemalloc memory allocator likes to bypass the libc when calling write, so
it calls the syscall directly. Let's make write available through this interface
as well.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

linux.cc

@@ -74,6 +74,19 @@ int futex(int *uaddr, int op, int val, const struct timespec *timeout,
 long syscall(long number, ...)
 {
     switch (number) {
+    case __NR_write: {
+        va_list args;
+        int arg1;
+        const void *arg2;
+        size_t arg3;
+        va_start(args, number);
+        arg1 = va_arg(args, typeof(arg1));
+        arg2 = va_arg(args, typeof(arg2));
+        arg3 = va_arg(args, typeof(arg3));
+        va_end(args);
+
+        return write(arg1, arg2, arg3);
+    }
     case __NR_gettid: return gettid();
     case __NR_clock_gettime: {
         va_list args;