[PATCH] ia64: properly include libunwind support during configuration

[PATCH] ia64: properly include libunwind support during configuration

By using the test `with_system_libunwind', libgcc can use either
in-house implementation or reference external libunwind symbols.
However, this breaks the static libgcc.a library, as in t-linux it
references unwind-compat.c, which turns some _Unwind_* symbols into
references of the corresponding symbols in libunwind, but libunwind does
not exist in some conditions (e.g. bootstrapping a toolchain). The
linker complains about `missing version node for symbol', since it can
not find the symbol it is referring to.

The unwind-compat.c module should only exist, if system libunwind is
being used. Also GCC itself should add -lunwind only if this condition
is met, too.

Implementing better control for whether to embed unwind implementation
into libgcc to fix this issue.

gcc/
	* config.gcc: limit -lunwind usage by testing if the system
	libunwind is being used.

libgcc/
	* config.host (ia64): include unwind-compat only if the system
	libunwind is being used.

	* config/ia64/t-linux-libunwind: include libgcc symver definition
	for libgcc symbols, since it bears the same role as t-linux
	(except libunwind); Include fde-glibc.c since the unwind
	implementation requires _Unwind_FindTableEntry in this file.

	* config/ia64/unwind-ia64.c: protect _Unwind_FindTableEntry inside
	inihbit_libc ifndefs to allow it to build with newlib or
	without proper headers.