Make strstr take a const char* as a needle instead of a char*

kernel/include/std/string.h

@@ -11,7 +11,7 @@ char* strncpy(char* dest, const char* src, size_t n);
 int strncmp(const char* a, const char* b, size_t n);
 char* strncat(char* dest, const char* src, size_t n);
 
-char* strstr(char* haystack, char* needle);
+char* strstr(char* haystack, const char* needle);
 
 void* memcpy(void* dest, const void* src, size_t n);
 void* memset(void* dest, int c, size_t n);

kernel/src/std/string.cpp

@@ -66,7 +66,7 @@ char* strcat(char* dest, const char* src)
     return dest;
 }
 
-char* strstr(char* haystack, char* needle)
+char* strstr(char* haystack, const char* needle)
 {
     size_t needle_size = strlen(needle);
     size_t haystack_size = strlen(haystack);