[FS#503] Build fails with CONFIG_KERNEL_GIT_CLONE_URI beig set

[LEDE Bugs]

The following task has a new comment added:

FS#503 - Build fails with CONFIG_KERNEL_GIT_CLONE_URI beig set
User who did this - Mirko Vogt (mirko)

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include/kernel-defaults.mk

doesn't seem the right place to dig, as either way - independendat of `CONFIG_KERNEL_GIT_CLONE_URI` being set or not, the tarball is assumed already being there.

My next candidate is the following line in `toolchain/kernel-headers/Makefile`:

PKG_SOURCE_URL:=$(LINUX_SITE)

LINUX_SITE gets set in include/kernel-defaults.mk and *only* if `CONFIG_KERNEL_GIT_CLONE_URI` is unset.

The regular kernel build takes this into account, while the kernel-headers-Makefile apparently doesn't.

In include/kernel-build.mk it states:

define BuildKernel
  $(if $(QUILT),$(Build/Quilt))
  $(if $(LINUX_SITE),$(call Download,kernel))
  $(if $(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI)),$(call Download,git-kernel))


while the kernel-headers-Makefile only relies on LINUX_SITE being set.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=503#comment1757