use std chr functions

The ones in std have overloads for const char/char.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/fs/StandardDirectory.cxx

@@ -164,7 +164,7 @@ ParseConfigLine(char *line, const char *dir_name, AllocatedPath &result_dir)
 	char *line_end;
 	// find end of the string
 	if (quoted) {
-		line_end = strrchr(line, '"');
+		line_end = std::strrchr(line, '"');
 		if (line_end == nullptr)
 			return true;
 	} else {

src/fs/Traits.hxx

@@ -196,7 +196,7 @@ struct PathTraitsUTF8 {
 		assert(p != nullptr);
 #endif
 
-		return strrchr(p, SEPARATOR);
+		return std::strrchr(p, SEPARATOR);
 	}
 
 #ifdef _WIN32