[XS] Change in coreboot[main]: payloads/external/Makefile.mk: Update linuxboot warning

[Maximilian Brune (Code Review)]

Attention is currently required from: Elyes Haouas, Martin L Roth.

Maximilian Brune has posted comments on this change by Maximilian Brune. ( https://review.coreboot.org/c/coreboot/+/85957?usp=email )

Change subject: payloads/external/Makefile.mk: Update linuxboot warning
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Patch Set 1:

(1 comment)

File payloads/external/Makefile.mk:

https://review.coreboot.org/c/coreboot/+/85957/comment/bf8e7d95_5dbec484?usp... :
PS1, Line 393: ifeq ($(CONFIG_LINUXBOOT_CROSS_COMPILE),y)
             : ifeq ($(CONFIG_LINUXBOOT_CROSS_COMPILE_PATH),"")
             :     # use coreboots cross toolchain
             :     CONFIG_LINUXBOOT_CROSS_COMPILE_PATH=$(CROSS_COMPILE_$(LINUXBOOT_CROSS_COMPILE_ARCH-y))
             : endif # CONFIG_LINUXBOOT_CROSS_COMPILE_PATH
             : else  # CONFIG_LINUXBOOT_CROSS_COMPILE
             : ifeq ($(CONFIG_PAYLOAD_LINUXBOOT),y)
             :     # only print warning when Linuxboot payload is actually selected
             :     $(warning "Using host toolchain to build Linuxboot")
             : endif # CONFIG_PAYLOAD_LINUXBOOT
             : endif # CONFIG_LINUXBOOT_CROSS_COMPILE
> I'm not sure, but about this: […]

It looks definitely more readable, but I noticed that you changed:
```
CONFIG_LINUXBOOT_CROSS_COMPILE_PATH=$(CROSS_COMPILE_$(LINUXBOOT_CROSS_COMPILE_ARCH-y))
```
to
```
CONFIG_LINUXBOOT_CROSS_COMPILE_PATH := $(CROSS_COMPILE_$(LINUXBOOT_CROSS_COMPILE_ARCH))
```
(notice the missing -y at the end)

I am also not sure if
```
ifeq ($(CONFIG_LINUXBOOT_CROSS_COMPILE_PATH),"")
```
is the same as:
```
ifeq ($(strip $(CONFIG_LINUXBOOT_CROSS_COMPILE_PATH)),)
```
specifically I am not sure if "" (empty string) is the same as 'nothing' in makefile syntax.