Fixed compile errors for STM32 boards

[Silveryard]

For stm32 (like the STM32F103C8T6 aka BluePill) we need to manually include stdarg.h.
Also avr/pgmspace.h does not define vsnprintf_P so this has to be done manually.

In the second commit I fixed some compiler warnings. There´s still 2 left though regarding a possible buffer overflow in EspDrv::sendData:

.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp: In static member function 'static bool EspDrv::sendData(uint8_t, const uint8_t*, uint16_t)':
.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:803:6: warning: 'sprintf' may write a terminating nul past the end of the destination [-Wformat-overflow=]
bool EspDrv::sendData(uint8_t sock, const uint8_t *data, uint16_t len)
^~~~~~
In file included from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/WString.h:29:0,
from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/wirish.h:47,
from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/Arduino.h:30,
from .piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:19:
C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/avr/pgmspace.h:28:37: note: 'sprintf' output between 15 and 21 bytes into a destination of size 20
#define sprintf_P(s, f, ...) sprintf((s), (f), __VA_ARGS__)
~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:808:2: note: in expansion of macro 'sprintf_P'
sprintf_P(cmdBuf, PSTR("AT+CIPSEND=%d,%u"), sock, len);
^~~~~~~~~
.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp: In static member function 'static bool EspDrv::sendData(uint8_t, const __FlashStringHelper*, uint16_t, bool)':
.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:831:6: warning: 'sprintf' may write a terminating nul past the end of the destination [-Wformat-overflow=]
bool EspDrv::sendData(uint8_t sock, const __FlashStringHelper *data, uint16_t len, bool appendCrLf)
^~~~~~
In file included from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/WString.h:29:0,
from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/wirish.h:47,
from C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/Arduino.h:30,
from .piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:19:
C:\users\sebif\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/avr/pgmspace.h:28:37: note: 'sprintf' output between 15 and 21 bytes into a destination of size 20
#define sprintf_P(s, f, ...) sprintf((s), (f), __VA_ARGS__)
~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
.piolibdeps\WiFiEsp\src\utility\EspDrv.cpp:837:2: note: in expansion of macro 'sprintf_P'
sprintf_P(cmdBuf, PSTR("AT+CIPSEND=%d,%u"), sock, len2);
^~~~~~~~~

[aster94]

I can confirm that this fixes the problem, @bportaluri also note that the problem is not relevant only to stm32 but also to others, see: #55
the above fix doesn't break compile compatibility on arduino UNO

[hawkliao]

I've added some updates in the #define in order to be compatible to stm32duino, with Blue Pill:
http://dan.drown.org/stm32duino/package_STM32duino_index.json

The updates:

#if defined(ARDUINO_ARCH_STM32) || defined (STM32_MCU_SERIES)
//For va_start
#include <stdarg.h>

//vsnprintf_P is not defined in avr/pgmspace.h for ststm32-maple
#define vsnprintf_P vsnprintf
#endif