libgcc for boot environment isn't always present and compatible.
libgcc is often absent if endianness or bit-size at boot is different
from running OS.
libgcc may use optimised opcodes that aren't available on boot time.
So instead of relying on libgcc shipped with the compiler, supply
the functions in GRUB directly.
Tests are present to ensure that those replacement functions behave the
way compiler expects them to.

Previously we supplied only unsigned divisions on platforms that need software
division.
Yet compiler may itself use a signed division. A typical example would be a
difference between 2 pointers which involves division by object size.

Fixes ARM compilation

In file included from ./include/grub/dl.h:23:0,
                 from grub-core/lib/libgcrypt-grub/cipher/rfc2268.c:3:
./include/grub/list.h:34:18: warning: conflicting types for 'grub_list_push' [en
abled by default]
 void EXPORT_FUNC(grub_list_push) (grub_list_t *head, grub_list_t item);
                  ^
./include/grub/symbol.h:68:25: note: in definition of macro 'EXPORT_FUNC'
 # define EXPORT_FUNC(x) x
                         ^
In file included from ./include/grub/fs.h:30:0,
                 from ./include/grub/file.h:25,
                 from ./grub-core/lib/posix_wrap/stdio.h:23,
                 from c:\mingw\include\libintl.h:314,
                 from ./include/grub/i18n.h:33,
                 from ./include/grub/misc.h:27,
                 from ./include/grub/list.h:25,
                 from ./include/grub/dl.h:28,
                 from grub-core/lib/libgcrypt-grub/cipher/rfc2268.c:3:
./include/grub/partition.h:106:3: note: previous implicit declaration of 'grub_l
ist_push' was here
   grub_list_push (GRUB_AS_LIST_P (&grub_partition_map_list),
   ^
list.h needs just ATTRIBUTE_ERROR from misc.h; split compiler features
into separate file grub/compiler.h and include it instead.

	Some compilers don't support it.

	using not very significant $target_os.

	Export abort () when compiling with clang.

	__sparc__ as __sparc64__ isn't actually defined.

	On upcoming arm64 port libgcc ctz* are not usable in standalone
	environment. Since we need ctz* for this case and implementation is
	in C we may as well use it on all concerned platforms.

GRUB_UTIL case.
* include/grub/misc.h: Likewise.

	helper functions are needed for thumb.

	* grub-core/kern/misc.c (__bzero) [__APPLE__]: New function.

	(grub_boot_time): Likewise.

	strncpy.
	* grub-core/fs/jfs.c (grub_jfs_lookup_symlink): Likewise.
	* grub-core/kern/misc.c (grub_strncpy): Move from here ...
	* include/grub/misc.h (grub_strncpy): ... to here. Make inline.
	* grub-core/net/net.c (grub_net_addr_to_str): Use COMPILE_TIME_ASSERT
	+ strcpy rather than strncpy.

	more appropriate functions.

	* include/grub/misc.h: Remove strncat.
	* grub-core/lib/posix_wrap/string.h: Likewise.

	* include/grub/misc.h (grub_isprint): ... here. Make inline.

	Saves 20 bytes on compressed image due to remving exporting.

	* include/grub/emu/misc.h: Likewise.

	template since our functions are independent of libc.

	tampered with after verification was done.

	into account when calculating radius.

	present. Remove symbols used for trampolines to make
	link fail if trampolines are present.

	* include/grub/misc.h (ATTRIBUTE_ERROR): Make into noreturn attribute
	on older compiler.

	(memmove) [__APPLE__]: Likewise.
	(memcpy) [__APPLE__]: Likewise.
	(memset) [__APPLE__]: Likewise.
	* grub-core/kern/misc.c (memcmp) [__APPLE__]: Likewise.
	(memmove) [__APPLE__]: Likewise.
	(memcpy) [__APPLE__]: Likewise.
	(memset) [__APPLE__]: Likewise.

	per common usage and preffered in several parts of code.
	(grub_memcmp): Likewise.
	(grub_strncmp): Likewise.
	* include/grub/misc.h (grub_strcasecmp): Likewise.
	(grub_strncasecmp): Likewise.
	* Makefile.util.def (cmp_test): New test.
	(grub_script_strcmp): Likewise.
	* tests/cmp_unit_test.c: New file.
	* tests/grub_script_strcmp.in: Likewise.
	* grub-core/fs/hfsplus.c (grub_hfsplus_cmp_catkey): Add a comment.

	* grub-core/loader/i386/linux.c (grub_cmd_initrd): Align initrds at 4.
	* grub-core/loader/i386/pc/linux.c (grub_cmd_initrd): Likewise.
	* grub-core/loader/ia64/efi/linux.c (grub_cmd_initrd): Likewise.
	* grub-core/loader/mips/linux.c (grub_cmd_initrd): Likewise.
	* grub-core/loader/powerpc/ieee1275/linux.c (grub_cmd_initrd): Likewise.
	* grub-core/loader/sparc64/ieee1275/linux.c (grub_cmd_initrd): Likewise.

	* include/grub/misc.h (grub_stpcpy): ... to here. Inlined.

	NEED_REGISTER_FRAME_INFO in GRUB_UTIL.