LibC: Implement strchrnul()

Author: https://github.com/shannonbooth
Commit: https://github.com/SerenityOS/serenity/commit/a52b3e8f2a4
Pull-request: https://github.com/SerenityOS/serenity/pull/1214
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/bugaevc
Reviewed-by: https://github.com/willmcpherson2

Libraries/LibC/string.cpp

@@ -297,6 +297,15 @@ char* strchr(const char* str, int c)
     }
 }
 
+char* strchrnul(const char* str, int c)
+{
+    char ch = c;
+    for (;; ++str) {
+        if (*str == ch || !*str)
+            return const_cast<char*>(str);
+    }
+}
+
 void* memchr(const void* ptr, int c, size_t size)
 {
     char ch = c;

Libraries/LibC/string.h

@@ -49,6 +49,7 @@ char* strndup(const char*, size_t);
 char* strcpy(char* dest, const char* src);
 char* strncpy(char* dest, const char* src, size_t);
 char* strchr(const char*, int c);
+char* strchrnul(const char*, int c);
 char* strstr(const char* haystack, const char* needle);
 char* strrchr(const char*, int c);
 char* strcat(char* dest, const char* src);