libc: Implement strrchr()

libs/libc/include/string.h

@@ -43,6 +43,9 @@ extern "C"
     /* Returns a pointer to the first occurrence of the character c in str, or NULL if it is not found. */
     char* strchr(const char* str, int c);
 
+    /* Returns a pointer to the last occurrence of the character c in str, or NULL if it is not found. */
+    char* strrchr(const char* str, int c);
+
     /* Concatenates the string src into dest. This function is unsafe, use strncat instead. */
     __lc_deprecated("strcat is unsafe and should not be used; use strncat instead") char* strcat(char* dest,
                                                                                                  const char* src);

libs/libc/src/string.cpp

@@ -133,6 +133,14 @@ extern "C"
         return NULL;
     }
 
+    char* strrchr(const char* str, int c)
+    {
+        const char* s = str + strlen(str);
+        while (s != str && *str != (char)c) str--;
+        if (s != str) return const_cast<char*>(s);
+        return NULL;
+    }
+
     void* bzero(void* buf, size_t n)
     {
         return memset(buf, 0, n);