At the very end of compilation under the Arduino IDE, I received these loader errors:

/home/digysol/arduino-1.8.0/hardware/tools/arm/bin/../lib/gcc/arm-none-eabi/4.8.4/../../../../arm-none-eabi/lib/armv7e-m/libc.a(lib_a-openr.o): In function `_open_r':
openr.c.text._open_r+0x10): undefined reference to `_open'
/home/digysol/arduino-1.8.0/hardware/tools/arm/bin/../lib/gcc/arm-none-eabi/4.8.4/../../../../arm-none-eabi/lib/armv7e-m/libc.a(lib_a-writer.o): In function `_write_r':
writer.c.text._write_r+0x10): undefined reference to `_write'
collect2: error: ld returned 1 exit status
Error compiling for board Teensy 3.2 / 3.1.

BTW, I get the same error if I select the Teensy 3.5 or 3.6 boards.

What could induce these errors in the source ?