[PATCH v3] kbuild: drop reliance on echo -e extension for DT fragments

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

We are using echo -e, so the \n in the string being echo'd are
interpreted. As -e is not POSIX and dash doesn't provide it,
we use a strange /usr/bin/env echo -e construct hoping that
whatever non-builtin echo is first in the search path supports -e.

As the new lines are just used to separate CPP directives, we can
just pass the directives as $(CPP) flags. This has the same result,
but is portable and avoids NixOS complaining when building barebox.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
v2 -> v3:
  - drop comment around $(pound) use, which no longer applies
  - reword commit message title and fix typo in body (Sascha)
  - use cpp /dev/null instead of empty echo | cpp (Sascha)
v1 -> v2:
  - drop echo -e eltogether after Sascha pointed out why it needs
    /usr/bin/env.
---
 scripts/Makefile.lib | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 4deaa5dfa73c..51beff56aeb8 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -371,9 +371,8 @@ $(obj)/%.dtb.z: $(obj)/%.dtb FORCE
 
 dts-frags = $(subst $(quote),,$(CONFIG_EXTERNAL_DTS_FRAGMENTS))
 quiet_cmd_dtc = DTC     $@
-# For compatibility between make 4.2 and 4.3
-cmd_dtc = /usr/bin/env echo -e '$(pound)define $(subst -,_,$(*F))_dts 1\n'$(foreach f,$< $(2),'$(pound)include "$(f)"\n') | \
-	$(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) - ; \
+cmd_dtc = $(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) \
+	-D'$(subst -,_,$(*F))_dts=1' $(foreach f,$< $(2),-include '$(f)') /dev/null ; \
 	$(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 \
 		-i $(srctree)/arch/$(SRCARCH)/dts $(DTC_FLAGS) \
 		-i $(srctree)/dts/src/$(SRCARCH) \
-- 
2.39.2