PowerPC was the one outlier that defined both ELF_ARCH and
ELF_MACHINE; ELF_ARCH was defined incorrectly, necessitating
the definition of elf_check_arch.
However, the elf file header field in question is called
e_machine, so ELF_MACHINE is in fact the better name.
Mechanically change most target/target_elf.h files,
then adjust ppc/target_elf.h manually.
Do not provide a default for ELF_MACHINE.
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>