update:
with some lib source fixes now the example from GitHub - jrowberg/i2cdevlib: I2C device library collection for AVR/Arduino or other C++-based MCUs also compiles for ARM Cortex M0 and M4 cpus,.
By theory, it also provides yaw, pitch, and roll.
Unfortunately the program often hangs up and gets stuck, it also needs an interrupt pin (which is actualy a problem because my Adafruit boards have extremely few free pins), and the calculated yaw value is still sort of unstable.
Does someone know a different lib which provides yaw, pitch, and roll and which is suitable for ARM cores, too?