[PATCH 1/4] Makefile: don't error out under DC_SHA1_EXTERNAL if DC_SHA1_SUBMODULE=auto

Fix a logic error in the initial introduction of DC_SHA1_EXTERNAL. If
git.git has a sha1collisiondetection submodule checked out the logic
to set DC_SHA1_SUBMODULE=auto would interact badly with the check for
whether DC_SHA1_SUBMODULE was set.

It would error out, meaning that there's no way to build git with
DC_SHA1_EXTERNAL=YesPlease without deinit-ing the submodule.

Instead, adjust the logic to only fire if the variable is to something
else than "auto" which would mean it's a mistake on the part of
whoever's building git, not just the Makefile tripping over its own
logic.

1. 3964cbbb5c ("sha1dc: allow building with the external sha1dc
   library", 2017-08-15)
2. cac87dc01d ("sha1collisiondetection: automatically enable when
   submodule is populated", 2017-07-01)

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index e53750ca01..8fe8278126 100644
--- a/Makefile
+++ b/Makefile

@@ -1497,7 +1497,9 @@ else
 	LIB_OBJS += sha1dc_git.o
 ifdef DC_SHA1_EXTERNAL
 	ifdef DC_SHA1_SUBMODULE
+ifneq ($(DC_SHA1_SUBMODULE),auto)
 $(error Only set DC_SHA1_EXTERNAL or DC_SHA1_SUBMODULE, not both)
+endif
 	endif
 	BASIC_CFLAGS += -DDC_SHA1_EXTERNAL
 	EXTLIBS += -lsha1detectcoll

-- 
2.15.0.403.gc27cc4dac6