-Wunreachable-code has been a no-op since GCC 4.5; GRUB hasn't been
compiled with it since 2012; and GCC 6 produces "error:
'-Wunreachable-code' is not an option that controls warnings" for these.

Fixes Debian bug #812047.

	condition to avoid possibly infinite loops.
	* grub-core/lib/pbkdf2.c (grub_crypto_pbkdf2): Likewise.
	* grub-core/lib/xzembed/xz_dec_bcj.c (bcj_powerpc): Likewise.

	* conf/Makefile.common (CFLAGS_GNULIB): Add -Wno-redundant-decls
	-Wno-unreachable-code -Wno-conversion -Wno-old-style-definition.
	* configure.ac (HOST_CFLAGS): Add bunch of -W arguments.
	(TARGET_CFLAGS): Likewise.
	(HOST_CFLAGS): Add -Werror unless --disable-werror is activated.
	* grub-core/Makefile.core.def (decompressor_xz): Add
	-Wno-unreachable-code.
	(normal): Add -Wno-redundant-decls.
	(xzio): Add -Wno-unreachable-code.
	(lzopio): Add -Wno-redundant-decls -Wno-error.
	* grub-core/commands/acpi.c: Add exception to -Wcast-align.
	* grub-core/commands/lsacpi.c: Add exception to -Wcast-align.
	* grub-core/gensymlist.sh: Add exception to -Wmissing-format-attribute.
	* grub-core/kern/dl.c: Add exception to -Wcast-align.
	* grub-core/kern/efi/efi.c (grub_efi_modules_addr): Likewise.
	* grub-core/kern/i386/coreboot/init.c: Add exception to
	-Wsuggest-attribute=noreturn.
	* grub-core/kern/ia64/dl.c: Add exception to -Wcast-align.
	* grub-core/kern/ia64/dl_helper.c: Likewise.
	* grub-core/kern/mips/dl.c: Likewise.
	* grub-core/kern/sparc64/dl.c: Likewise.
	* grub-core/lib/LzmaEnc.c: Add exception to -Wshadow.
	* grub-core/lib/libgcrypt_wrap/cipher_wrap.h (memcpy): Likewise.
	(memcmp): Likewise.
	* grub-core/lib/pbkdf2.c: Add exception to -Wunreachable-code.
	* grub-core/loader/ia64/efi/linux.c: Add exception to -Wcast-align.
	* grub-core/loader/mips/linux.c: Likewise.
	* grub-core/loader/multiboot_elfxx.c: Likewise.
	* grub-core/script/parser.y: Add exception to -Wunreachable-code.
	* grub-core/video/sm712.c: Add exception to -Wcast-align.
	* util/import_gcry.py: Add -Wno-cast-align to modules checked by hand.
	* grub-core/font/font.c (grub_font_loader_init): Add explicit cast and
	fixme.
	* grub-core/fs/iso9660.c (grub_iso9660_iterate_dir): Likewise.
	* grub-core/kern/i386/multiboot_mmap.c (grub_machine_mmap_init):
	Fix prototype.

	guidelines.

	* grub-core/kern/dl.c (grub_dl_check_license): New function.
	(grub_dl_load_core): Use grub_dl_check_license.
	* include/grub/dl.h (GRUB_MOD_SECTION): New macro.
	(GRUB_MOD_LICENSE): Likewise.
	(GRUB_MOD_DUAL_LICENSE): Likewise.
	All modules updated.