Error in gcc_current_sp in compiler_abstraction.h

[FelixGruen]

When I try to build a C programm for the micro:bit with yotta, it tells me:

compiler_abstraction.h:85:30: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'asm'
         register unsigned sp asm("sp");
                              ^~~

I followed the installation guide on https://lancaster-university.github.io/microbit-docs/offline-toolchains/ for the general tool chain and installed yotta according to http://yottadocs.mbed.com/ with the gcc-arm-embedded package from team-gcc-arm-embedded/ppa.

And I'm using the 64-bit version of Ubuntu 14.04 LTS.

The complete error message is:

info: generate for target: bbc-microbit-classic-gcc 0.2.3 at /my_project/yotta_targets/bbc-microbit-classic-gcc
warning: subdirectory "test" of my_project 0.0.0 at /my_project was ignored because it doesn't appear to contain any source files
GCC version is: 6.2.1
suppressing warnings from ble-nrf51822
suppressing warnings from nrf51-sdk
fatal: Not a git repository (or any of the parent directories): .git
fatal: Not a git repository (or any of the parent directories): .git
suppressing ALL warnings from mbed-classic, ble, ble-nrf51822 & nrf51-sdk
-- Configuring done
-- Generating done
-- Build files have been written to: /my_project/build/bbc-microbit-classic-gcc
[1/2] Building C object source/CMakeFiles/my_project.dir/my_project/source/start.c.o
FAILED: /usr/bin/arm-none-eabi-gcc  -DYOTTA_MODULE_NAME=my_project -Dmy_project_EXPORTS -std=c99 -fno-exceptions -fno-unwind-tables [...]
In file included from /my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/nrf.h:43:0,
                 from /my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/cmsis.h:10,
                 from /my_project/yotta_modules/mbed-classic/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/objects.h:19,
                 from /my_project/yotta_modules/mbed-classic/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/TARGET_NRF51_MICROBIT/device.h:55,
                 from /my_project/yotta_modules/mbed-classic/api/platform.h:21,
                 from /my_project/yotta_modules/mbed-classic/api/mbed.h:21,
                 from /my_project/yotta_modules/microbit/inc/MicroBit.h:29,
                 from /my_project/source/start.c:1:
/my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/compiler_abstraction.h: In function 'gcc_current_sp':
/my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/compiler_abstraction.h:85:30: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'asm'
         register unsigned sp asm("sp");
                              ^~~
/my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/compiler_abstraction.h:85:30: warning: implicit declaration of function 'asm' [-Wimplicit-function-declaration]
/my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/compiler_abstraction.h:86:16: error: 'sp' undeclared (first use in this function)
         return sp;
                ^~
/my_project/yotta_modules/mbed-classic/targets/cmsis/TARGET_NORDIC/TARGET_MCU_NRF51822/compiler_abstraction.h:86:16: note: each undeclared identifier is reported only once for each function it appears in
In file included from /my_project/yotta_modules/mbed-classic/api/mbed.h:21:0,
                 from /my_project/yotta_modules/microbit/inc/MicroBit.h:29,
                 from /my_project/source/start.c:1:
/my_project/yotta_modules/mbed-classic/api/platform.h: At top level:
/my_project/yotta_modules/mbed-classic/api/platform.h:25:19: fatal error: cstddef: No such file or directory
 #include <cstddef>
                   ^
compilation terminated.
ninja: build stopped: subcommand failed.
error: command ['ninja'] failed

The exact commands I used were:

yt init
yt target bbc-microbit-classic-gcc
yt install lancaster-university/microbit
yt build

If I build it as a C++ project by changing the file ending to cpp it builds without problems.