Don't link the kernel as a shared lib on ARM

We have the same problem as on x86_64: posiiton dependant code isn't
allowed in shared libraries. Since Kernel.so is not used at runtime,
we can use the same hack as on x86_64, and use elfedit to make the
linker think our kernel is a shared library.

src/system/kernel/Jamfile

@@ -139,7 +139,7 @@ KernelLd kernel_$(TARGET_ARCH) :
 	:
 ;
 
-if $(HAIKU_ARCH) = x86_64 {
+if $(HAIKU_ARCH) in x86_64 arm {
 	# Cannot relink everything as a shared object on x86_64 as shared library
 	# code is required to be position-independent. Instead create a copy of the
 	# executable kernel image and change the ELF header type to DYN. A bit of