Do a pass of compiler warning fixes.

This is really making me question not using 64-bit integers more.

LibC/stdio.cpp

@@ -9,6 +9,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <AK/printf.cpp>
+#include <AK/StdLibExtras.h>
 #include <Kernel/Syscall.h>
 
 extern "C" {
@@ -405,6 +406,7 @@ FILE* freopen(const char* pathname, const char* mode, FILE* stream)
 
 FILE* fdopen(int fd, const char* mode)
 {
+    UNUSED_PARAM(mode);
     // FIXME: Verify that the mode matches how fd is already open.
     if (fd < 0)
         return nullptr;

LibC/stdlib.cpp

@@ -133,7 +133,7 @@ void free(void* ptr)
         return;
     }
 
-    for (unsigned i = header->first_chunk_index; i < (header->first_chunk_index + header->chunk_count); ++i)
+    for (int i = header->first_chunk_index; i < (header->first_chunk_index + header->chunk_count); ++i)
         s_malloc_map[i / 8] &= ~(1 << (i % 8));
 
     s_malloc_sum_alloc -= header->chunk_count * CHUNK_SIZE;
@@ -473,7 +473,7 @@ long strtol(const char* str, char** endptr, int base)
     } else if (neg)
         acc = -acc;
     if (endptr)
-        *endptr = (char*)(any ? s - 1 : str);
+        *endptr = const_cast<char*>((any ? s - 1 : str));
     return acc;
 }
 

LibC/string.cpp

@@ -202,10 +202,10 @@ char* strchr(const char* str, int c)
 void* memchr(const void* ptr, int c, size_t size)
 {
     char ch = c;
-    char* cptr = (char*)ptr;
+    auto* cptr = (const char*)ptr;
     for (size_t i = 0; i < size; ++i) {
         if (cptr[i] == ch)
-            return cptr + i;
+            return const_cast<char*>(cptr + i);
     }
     return nullptr;
 }
@@ -358,7 +358,7 @@ char* strpbrk(const char* s, const char* accept)
 {
     while (*s)
         if(strchr(accept, *s++))
-            return (char*)--s;
+            return const_cast<char*>(--s);
     return nullptr;
 }
 

LibC/unistd.cpp

@@ -83,7 +83,7 @@ int execl(const char* filename, const char* arg0, ...)
     }
     va_end(ap);
     args.append(nullptr);
-    return execve(filename, (char* const *)args.data(), environ);
+    return execve(filename, const_cast<char* const*>(args.data()), environ);
 }
 
 uid_t getuid()