FIX: fix the compiling error under macos for previous patches

/Users/ci.slave/slicer/patch_build/1/bamboo_slicer/src/libslic3r/GCode/GCodeProcessor.cpp:486:33: error: cannot pass non-trivial object of type 'std::string' (aka 'basic_string<char, char_traits<char>, allocator<char>>') to variadic function; expected type from format string was 'char *' [-Wnon-pod-varargs]
                                  get_time_dhms(machine.time));
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~

github pull request: bambulab#3360
Change-Id: If13ee145b20ef9532b23a58bb3b0a29f30d8c0a8

Change-Id: I98fd87417c432c3afae67a3d2bc29c79f8bffa3c

src/libslic3r/GCode/GCodeProcessor.cpp

@@ -483,7 +483,7 @@ void GCodeProcessor::TimeProcessor::post_process(const std::string& filename, st
                         if (!s_IsBBLPrinter) {
                             // Klipper estimator
                             sprintf(buf, "; estimated printing time (normal mode) = %s\n",
-                                get_time_dhms(machine.time));
+                                get_time_dhms(machine.time).c_str());
                             ret += buf;
                         } else {
                             // BBS estimator