[staging] ArduinoJson example and libc_replacements compiler warnings

[andig]

This is fyi- not sure there is any actual problem:

C:\Users\Arduino\libraries\ArduinoJson\src\JsonVariant.cpp:38:18: warning: always_inline function might not be inlinable [-Wattributes]
 FORCE_INLINE int parse<int>(const char *s) {
          ^
C:\Users\Arduino\libraries\ArduinoJson\src\JsonVariant.cpp:33:19: warning: always_inline function might not be inlinable [-Wattributes]
 FORCE_INLINE long parse<long>(const char *s) {
           ^
C:\Users\Arduino\libraries\ArduinoJson\src\JsonVariant.cpp:28:21: warning: always_inline function might not be inlinable [-Wattributes]
 FORCE_INLINE double parse<double>(const char *s) {
             ^
C:\Users\Arduino\libraries\ArduinoJson\src\JsonVariant.cpp:23:20: warning: always_inline function might not be inlinable [-Wattributes]
 FORCE_INLINE float parse<float>(const char *s) {
            ^
C:\Users\AppData\Roaming\Arduino15\packages\esp8266\hardware\esp8266\1.6.5-1160-gef26c5f\cores\esp8266\libc_replacements.c:408:22: warning: 'struct tm' declared inside parameter list [enabled by default]
 time_t mktime(struct tm *timp) {
              ^
C:\Users\AppData\Roaming\Arduino15\packages\esp8266\hardware\esp8266\1.6.5-1160-gef26c5f\cores\esp8266\libc_replacements.c:408:22: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]

[igrr]

I think the first 4 warnings should be reported in https://github.com/bblanchon/ArduinoJson.
The other two have been fixed in git (#740).