ARM:asm:io.h use static inline

When compiling u-boot with W=1 the extern inline void for
read* is likely causing the most noise. gcc / clang will
warn there is never a actual declaration for these functions.
Instead of declaring these extern make them static inline so
it is actually declared.

cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
common: board_f: cosmetic use __weak for leds

First of all this looks a lot better, but it also
prevents a gcc warning (W=1), that the weak function
has no previous prototype.

cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>

---
This likely causes some merge issues, but is so uggly it
deserves it.
ARM: bump minimum arch to armv4t when supported

U-boot typically uses an -march lower then actually supported
by the architecture to be backwards compatible with older
compilers. For armv4 this also causes problems occasionally,
like "selected processor does not support ARM mode `bx lr'".
Although this case is actually a llvm bug afaik, it should be
possible to correct it for GNU tools with --fix-v4bx, but that
seems to be bugged as well (at least I cannot get it working).

Since there is exactly 1 board in u-boot (jornada) which
actually is armv4, I propose to increase the arch for the
others to armv4t. As far as I can make some sense of ARM
versions the other chips should have these instructions.

cc: Albert Aribaud <albert.u.boot@aribaud.net>
Not-signed-off-since-rfc: Jeroen Hofstee <jeroen@myspectrum.nl>
board_r: ARM[64] do not set gd again

For ARM / ARM64 the relocation routines already updated
gd to the new value. Don't set it again. This allows
compilation with clang as it cannot update gd directly.
ARM: SPL: do not set gd again
cc-option: also detect unsupported warnings options

By default clang will echo a warning if a warning option is
unknown. Turning warnings into errors when polling for options
also catches such cases and prevents passing arguments to the
compiler which cause warnings.
ARM: make gd a function for clang

"clang does not support global register variables; this is
unlikely to be implemented soon because it requires additional
LLVM backend support" [1]

Workaround it by obtaining the value of gd/r9 by an inline
asm routine. Note there is no set routine added for ARM at the
moment, since most if not all updates of gd from c are actually
not needed for ARM.

[1] http://clang.llvm.org/docs/UsersManual.html
eabi_compat: add __aeabi_memcpy __aeabi_memset

---
fixes this:

common/libcommon.o: In function `env_callback_init':
/home/jeroen/software/u-boot/common/env_callback.c:47: undefined reference to `__aeabi_memset'
common/libcommon.o: In function `parse_stream_outer':
/home/jeroen/software/u-boot/common/hush.c:3154: undefined reference to `__aeabi_memset'
disk/libdisk.o: In function `get_device_and_partition':
/home/jeroen/software/u-boot/disk/part.c:596: undefined reference to `__aeabi_memcpy'
/home/jeroen/software/u-boot/disk/part.c:605: undefined reference to `__aeabi_memcpy'
fs/fat/libfat.o: In function `fat_set_blk_dev':
/home/jeroen/software/u-boot/fs/fat/fat.c:60: undefined reference to `__aeabi_memcpy'
fs/ubifs/libubifs.o: In function `ubifs_tnc_locate':
/home/jeroen/software/u-boot/fs/ubifs/tnc.c:1457: undefined reference to `__aeabi_memcpy'
fs/ubifs/libubifs.o: In function `tnc_insert':
/home/jeroen/software/u-boot/fs/ubifs/tnc.c:2008: undefined reference to `__aeabi_memcpy'
fs/ubifs/libubifs.o:/home/jeroen/software/u-boot/fs/ubifs/tnc.c:2333: more undefined references to `__aeabi_memcpy' follow
arm-linux-gnueabi-ld.bfd: BFD (GNU Binutils for Ubuntu) 2.23.2 assertion fail ../../bfd/elf32-arm.c:7683
arm-linux-gnueabi-ld.bfd: BFD (GNU Binutils for Ubuntu) 2.23.2 assertion fail ../../bfd/elf32-arm.c:7683
arm-linux-gnueabi-ld.bfd: error: required section '.rel.plt' not found in the linker script
arm-linux-gnueabi-ld.bfd: final link failed: Invalid operation
clang: workaround for generated constants

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.
common: Makefile: limit -Wa,--no-warn to powerpc
README.clang: build command with clang