ARM: 5776/1: Check compiler version and EABI support when adding ARM unwind support.

ARM unwind is known to compile only with EABI and not-buggy compilers.
The problem is not the unwinding information but the -fno-frame-pointer
option added as a result of !CONFIG_FRAME_POINTER.  Now we check the
compiler and raise a #warning in case of wrong compiler.

Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>