compiling multilib for arm cortex

[Timo Sintonen via D.gnu]

I have been trying to compile multilib for cortex-m0/m3/m4

I added this to gcc/config/arm/t-arm-elf:

MULTILIB_OPTIONS  += mcpu=cortex-m0/mcpu=cortex-m3/mcpu=cortex-m4 
  mfloat-abi=hard mfpu=fpv4-sp-d16
MULTILIB_DIRNAMES += cortex-m0 cortex-m3 cortex-m4
MULTILIB_REQUIRED += mcpu=cortex-m0
MULTILIB_REQUIRED += mcpu=cortex-m3
MULTILIB_REQUIRED += mcpu=cortex-m4
MULTILIB_EXTRA_OPTS += mthumb

The first line tells to build all combinations of those options 
but the next three lines telss to build only with these options. 
The last adds that option to all builds.

This works and makes three libraries with the correct cpu option.

This does not work although it should according to
https://gcc.gnu.org/onlinedocs/gccint/Target-Fragment.html

MULTILIB_OPTIONS  += mcpu=cortex-m0/mcpu=cortex-m3/mcpu=cortex-m4 
  mfloat-abi=hard mfpu=fpv4-sp-d16
MULTILIB_DIRNAMES += cortex-m0 cortex-m3 cortex-m4
MULTILIB_REQUIRED += mcpu=cortex-m0
MULTILIB_REQUIRED += mcpu=cortex-m3
MULTILIB_REQUIRED += 
mcpu=cortex-m4/mfloat-abi=hard/mfpu=fpv4-sp-d16
MULTILIB_EXTRA_OPTS += mthumb

After creating cortex-m4 directory the error message is:
././ is a directory

Does anybody have any idea or should I ask this in gcc list?