The Arduino IDE allows for external libraries to be added to support devices and functions not in the core setup. For details on creating libraries see the Arduino Library Specifications
In order that a library, that is specific to one architecture or board type is only compiled when a supporting board is setup, this specification has a setting for the architecture the library will work on. The library.properties file architecture setting is shortly going to be changed from a confusing arm name to a less confusing name of xmc, to avoid any confusions for those using multiple boards and architectures for third party libraries compatibility.
Currently third party and other external libraries use the library.properties architecture setting to define which board architecture the library is compiled for The XMC-for-Arduino current setting for up to V1.50 is -
architecture=arm
When creating or maintaining third party or external libraries please use library.properties architecture setting for versions V1.5.0 and above -
architecture=xmc,arm
The Arduino IDE on compilation will work out which one to use automatically, avoiding any strange updating issues. At a later stage to be announced, it will be recommended to change to
architecture=xmc
As all newer versions will be using architecture xmc.
If your library ALSO supports other boards and architectures, obviously leave those in as well.
Check XMC-for-Arduino Wiki for any additional information