[coreboot-gerrit] Change in coreboot[master]: Makefile: set and export SOURCE_DATE_EPOCH

[Patrick Georgi (Code Review)]

Attention is currently required from: Martin Roth.
Patrick Georgi has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51364 )

Change subject: Makefile: set and export SOURCE_DATE_EPOCH
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Patch Set 5: Code-Review+2

(1 comment)

File Makefile:

https://review.coreboot.org/c/coreboot/+/51364/comment/5f753bb2_3b09c305 
PS5, Line 27: SOURCE_DATE_EPOCH := $(shell $(top)/util/genbuild_h/genbuild_h.sh . | sed -n 's/^.define COREBOOT_BUILD_EPOCH>.*"(.*)".*/\1/p')
> I don't know if there is a better approach, however build. […]

There's certainly room for optimization, but let's defer that...