kernel/libc: fix putchar() (#616)

Author: willdurand

src/kernel/sys/k_write.c

@@ -12,14 +12,8 @@
 ssize_t k_write(int fd, const void* buf, size_t count)
 {
   if (fd == STDOUT || fd == STDERR) {
-    // TODO: Make the code in this block better.
-    const char* s = (const char*)buf;
-    if (count > strlen(s)) {
-      count = strlen(s);
-    }
-
     for (size_t i = 0; i < count; i++) {
-      arch_putchar(s[i]);
+      arch_putchar(((const char*)buf)[i]);
     }
 
     return count;

src/libc/putchar.c

@@ -4,6 +4,5 @@
 
 void putchar(char c)
 {
-  // Make sure we write a null-terminated string.
-  write(STDOUT_FILENO, (char[]){ c, '\0' }, 1);
+  write(STDOUT_FILENO, &c, 1);
 }