It seems there is a typo in recently added I2S header file. I mean i2s_lld.h file from os/hal/ports/STM32/LLD/SPIv1 directory:
========
#if STM32_I2S_USE_SPI2 && !defined(DOXYGEN)
extern I2SDriver I2SD2;
#endif
#if STM32_I2S_USE_I2S3 && !defined(DOXYGEN)
extern I2SDriver I2SD3;
#endif
========
The first check seems to be fine, but second one should be #if STM32_I2S_USE_SPI3 not #if STM32_I2S_USE_I2S3 I guess.
Diff:
Fixed in repository, thanks.