Add plumbing for building U-Boot with Link Time Optimizations.

When building with LTO, $(PLATFORM_LIBS) has to be in --whole-archive /
--no-whole-archive group, otherwise some functions declared in assembly
may not be resolved and linking may fail.

Note: clang may throw away linker list symbols it thinks are unused when
compiling with LTO. To force these symbols to be included, we refer to
them via the __ADDRESSABLE macro in a C file generated from compiled
built-in.o files before linking.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>

Currently generic-asm-offsets.h and asm-offsets.h are generated based
on U-Boot proper config options. The same asm-offsets headers are used
for building U-Boot SPL/TPL, which causes potential offset mismatch if
U-Boot proper has different config options from U-Boot SPL/TPL.

This commit adds:
  spl/include/generated/(generic-)asm-offsets.h
  tpl/include/generated/(generic-)asm-offsets.h

spl/include/generated/(generic-)asm-offsets.h is generated if
CONFIG_SPL=y, and included when building SPL.

tpl/include/generated/(generic-)asm-offsets.h is generated if
CONFIG_TPL=y, and included when building TPL.

They are created before Kbuild descends into SPL/TPL object directories
and builds $(obj)/dts/dt-platdata.o because $(obj)/dts/dt-platdata.c
includes a bunch of headers.

Prepend -I$(obj)/include to $(UBOOTINCLUDE) so (generic-)asm-offsets.h
is searched in {spl,tpl}/include/generated/.

Requested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

b42841b7bb62 kbuild: Get rid of KBUILD_STR
2aedcd098a94 kbuild: suppress annoying "... is up to date." message
9c8fa9bc08f6 kbuild: fix if_change and friends to consider argument order
ebf003f0cfb3 kbuild: Consolidate header generation from ASM offset information
2982c953570b kbuild: remove redundant $(wildcard ...) for cmd_files calculation
8a78756eb545 kbuild: create object directories simpler and faster
4d4b5c2e3b6e treewide: remove explicit rules for *offsets.s
01d509a48b46 kbuild: remove unimportant comments from ./Kbuild

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

$(always) is added to targets by scripts/Makefile.build.
Moreover, filechk does not need .*.cmd files.

Adding these two files to targets is redundant.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Use filechk to generate asm-offsets.h and generic-asm-offsets.h.
Based on a patch by Valdis Kletnieks.

Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Acked-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
[ imported from Linux Kernel, commit 70a4fd6c56d0,
  with adjustment for U-Boot ]
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

This line produces an extra comment line for generic-asm-offsets.h
and asm-offsets.h.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
[ imported from Linux Kernel, commit 343d3e6cc861,
  with modification of commit description ]
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

The rules "cmd_generic-offsets" and "cmd_offsets" are almost the
same. (The difference is only the include guards.)
They can be merged.

This commit is mostly inspired by the following commit of Linux.

    commit 39664e2f3cdef98f42437e903159a6044a1d99d6
    Author: Masahiro Yamada <yamada.m@jp.panasonic.com>
    Date:   Mon Jan 5 15:57:15 2015 +0900

        kbuild: merge bounds.h and asm-offsets.h rules

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

KBuild abuses the asm statement to write to a file and
clang chokes about these invalid asm statements. Hack it
even more by fooling this is actual valid asm code.

cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
cc: Tom Rini <trini@ti.com>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>

U-Boot has supported two kinds of asm-offsets.h.

One is generic for all architectures and its source is located at
./lib/asm-offsets.c.

The other is SoC specific and its source is under SoC directory.
The problem here is that only boards with SoC directory can use
the asm-offsets infrastructure.
Putting asm-offsets.c right under CPU directory does not work.

Now a new demand is coming. PowerPC folks want to use asm-offsets.
But no PowerPC boards have SoC directory.

It seems inconsistent that some boards add asm-offsets.c to SoC
directoreis and some to CPU directories.
It looks more reasonable to put asm-offsets.c under arch/$(ARCH)/lib.

This commit merges asm-offsets.c under SoC directories into
arch/$(ARCH)/lib/asm-offsets.c.

By the way, I doubt the necessity of some entries in asm-offsets.c.
I am leaving refactoring to the board maintainers.
Please check "TODO" in the comment blocks in
arch/{arm,nds32}/lib/asm-offsets.c.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Yuantian Tang <Yuantian.Tang@freescale.com>

Generate include/generated/generic-asm-offsets.h and
include/generated/asm-offsets.h in ./Kbuild.

This commit also changes the include guard.

Before this commit, __ASM_OFFSETS_H__ was used for both of them.
So we could not include generic-asm-offsets.h and asm-offsets.h
at the same time.

This commit renames the include guard of the former to
__GENERIC_ASM_OFFSETS_H__.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>