Add solutions

exercises/093_hello_c.zig

@@ -54,7 +54,7 @@ pub fn main() void {
     //
     // In this exercise we use 'write' to output 17 chars,
     // but something is still missing...
-    const c_res = write(2, "Hello C from Zig!", 17);
+    const c_res = c.write(2, "Hello C from Zig!", 17);
 
     // let's see what the result from C is:
     std.debug.print(" - C result is {d} chars written.\n", .{c_res});