nios2 target support in GCC was deprecated in GCC 14 as the
architecture has been EOL'ed by the vendor.  This patch removes the
entire port for GCC 15

There are still references to "nios2" in libffi and libgo.  Since those
libraries are imported into the gcc sources from master copies maintained
by other projects, those will need to be addressed elsewhere.

ChangeLog:
	* MAINTAINERS: Remove references to nios2.
	* configure.ac: Likewise.
	* configure: Regenerated.

config/ChangeLog:
	* mt-nios2-elf: Deleted.

contrib/ChangeLog:
	* config-list.mk: Remove references to Nios II.

gcc/ChangeLog:
	* common/config/nios2/*: Delete entire directory.
	* config/nios2/*: Delete entire directory.
	* config.gcc: Remove references to nios2.
	* configure.ac: Likewise.
	* doc/extend.texi: Likewise.
	* doc/install.texi: Likewise.
	* doc/invoke.texi: Likewise.
	* doc/md.texi: Likewise.
	* regenerate-opt-urls.py: Likewise.
	* config.in: Regenerated.
	* configure: Regenerated.

gcc/testsuite/ChangeLog:
	* g++.target/nios2/*: Delete entire directory.
	* gcc.target/nios2/*: Delete entire directory.
	* g++.dg/cpp0x/constexpr-rom.C: Remove refences to nios2.
	* g++.old-deja/g++.jason/thunk3.C: Likewise.
	* gcc.c-torture/execute/20101011-1.c: Likewise.
	* gcc.c-torture/execute/pr47237.c: Likewise.
	* gcc.dg/20020312-2.c: Likewise.
	* gcc.dg/20021029-1.c: Likewise.
	* gcc.dg/debug/btf/btf-datasec-1.c: Likewise.
	* gcc.dg/ifcvt-4.c: Likewise.
	* gcc.dg/stack-usage-1.c: Likewise.
	* gcc.dg/struct-by-value-1.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-33.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-34.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-35.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-36.c: Likewise.
	* lib/target-supports.exp: Likewise.

libgcc/ChangeLog:
	* config/nios2/*: Delete entire directory.
	* config.host: Remove refences to nios2.
	* unwind-dw2-fde-dip.c: Likewise.