ARM: SPL: do not set gd again

Just before calling board_init_f, crt0.S has already
reserved space for the initial gd on the stack. There
should be no need to allocate it again.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
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.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
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

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
eabi_compat: add __aeabi_memcpy __aeabi_memset

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
---
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.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Makefile: default to cc for host compiler

Since the host compiler might not be gcc but e.g. clang
default to cc to invoke it.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
README.clang: build command with clang

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>