[SDK] Minor improvements to CRT, RTL, and headers

Signed-off-by: Quinn Stephens <quinn@osmora.org>

SDK/CRT/STRING/str.c

@@ -24,9 +24,11 @@ strlen (
     const char *ptr;
 
     ptr = str;
-    while (*ptr++);
+    while (*ptr) {
+        ptr++;
+    }
 
-    return ptr - str - sizeof(char);
+    return ptr - str;
 }
 
 size_t
@@ -36,12 +38,14 @@ strnlen (
     )
 
 {
-    size_t len;
+    const char *ptr;
 
-    len = 0;
-    while (len < maxlen && str[len++]);
+    ptr = str;
+    while (maxlen-- && *ptr) {
+        ptr++;
+    }
 
-    return len - sizeof(char);
+    return ptr - str;
 }
 
 int