[M] Change in coreboot[main]: Makefile.mk: Add a common link_stage function and use it

[Arthur Heymans (Code Review)]

Attention is currently required from: Julius Werner, Jérémy Compostella, Philipp Hug, Ron Minnich.

Hello Julius Werner, Jérémy Compostella, Philipp Hug, Ron Minnich,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/83574?usp=email

to look at the new patch set (#2).

Change subject: Makefile.mk: Add a common link_stage function and use it
......................................................................

Makefile.mk: Add a common link_stage function and use it

A few differences with the original link targets:
- 'libs' is now supported on all arch even though only x86 uses it
- compiler_rt is included on arch that previously did not (arm). This
  however has no impact as there compiler_rt is not defined for those arch
  in xcompile
- LIBGCC_FILE_NAME_bootblock is not included, but this was not defined
  anywhere so this is a noop
- the x86 --oformat is dropped as it is not needed.

Change-Id: I64f7686894c99732d06972e7ba327061db6d7c44
Signed-off-by: Arthur Heymans 
---
M Makefile.mk
M src/arch/arm/Makefile.mk
M src/arch/arm64/Makefile.mk
M src/arch/ppc64/Makefile.mk
M src/arch/riscv/Makefile.mk
M src/arch/x86/Makefile.mk
6 files changed, 30 insertions(+), 92 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/74/83574/2