stdio, string, platform: fix a bug in printf() involving chars

Because we were previously converting the bytes in the format
string into Rust's char type and then printing that using the
format machinery, byte values that were not valid single-byte
UTF-8 characters failed to print correctly.  I found this while
trying to implement qsort() because the output of my test program
was mysteriously incorrect despite it working when I used glibc.

src/string/src/lib.rs

@@ -58,12 +58,7 @@ pub unsafe extern "C" fn memcmp(s1: *const c_void, s2: *const c_void, n: usize)
 
 #[no_mangle]
 pub unsafe extern "C" fn memcpy(s1: *mut c_void, s2: *const c_void, n: usize) -> *mut c_void {
-    let mut i = 0;
-    while i < n {
-        *(s1 as *mut u8).offset(i as isize) = *(s2 as *const u8).offset(i as isize);
-        i += 1;
-    }
-    s1
+    platform::memcpy(s1, s2, n)
 }
 
 #[no_mangle]
@@ -385,10 +380,3 @@ pub extern "C" fn strtok_r(
 pub extern "C" fn strxfrm(s1: *mut c_char, s2: *const c_char, n: usize) -> size_t {
     unimplemented!();
 }
-
-/*
-#[no_mangle]
-pub extern "C" fn func(args) -> c_int {
-    unimplemented!();
-}
-*/