ARM: Change ABI to not use short enums

[Sebastian Huber]

Whether enums are short or not is left open in the ARM EABI. On Linux and FreeBSD no short enums are used. Otherwise short enums are enabled by default.

Short enums may cause hard to find issues with 3rd party software, since the are quite unusual in general, e.g.

​https://git.rtems.org/rtems-libbsd/commit/freebsd/include/rpc?id=9880635f2e642380b69b85e00271649b3a2fc2de

The data and structure layout may suddenly change in case enumeration values are added/removed. The benefit of short enums is probably not worth the trouble, since the packed compiler attribute can be used to individually make an enum short.

The reason for not choosing no short enums during the ARM EABI introduction was an issue with Newlib. This is addressed with the following patch:

​https://sourceware.org/ml/newlib/2017/msg00238.html

[Sebastian Huber]

GCC changes are in place:

​https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=246753
​https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=246754

[Sebastian Huber]

GCC website update done (GCC 6.4 changes show up once released):

​https://gcc.gnu.org/gcc-6/changes.html
​https://gcc.gnu.org/gcc-7/changes.html

[Sebastian Huber]

Fixed due to change to GCC 7.1.

[Sebastian Huber]

Milestone renamed