Hi PacoLM,
(This is the quickest and easiest method for me to communicate with you, we can always delete the thread when we are done)
I have slept on it

we need to find a starting point (this is all hypothetical and subjective) from what is known:
The compile error is related to an arm register.
The application source code comes from a reputable place
I surmise:
The cpu register information is imparted from the included header files belonging to the compiler.
It is unlikely to be a coding error.
That leads me:
Both the application and the compiler are multi platform, possibly making it a porting issue (of either one).
Both the application and the compiler have been through numerous generations (and subsequently, header file changes).
I suggest you investigate the second issue first, as I believe it to be the most likely.
See if you can track down which version of which compiler was used by the application developers for the particular version of the application source that you are trying to compile.
If you can install the same compiler, see what results you get using it.
If you can't, investigate any differences between the compiler header files against the version you are using.
That's all I can come up with on the information you have given me.
I will need the specific information required to duplicate your development system to be any further help (where and how you got the application source, compiler, diistro and the changes made to it, etc).
Bear in mind, diagnosing errors at a distance of 1262km is never an easy thing, I may be leading you up the garden path.