treewide: ensure one of the appropriate headers is sourced first

We had several C files ignoring the rule to include one of the
appropriate headers first; fix that.

While at it, the rule in Documentation/CodingGuidelines about which
header to include has also fallen out of sync, so update the wording to
mention other allowed headers.

Unfortunately, C files in reftable/ don't actually follow the previous
or updated rule.  If you follow the #include chain in its C files,
reftable/system.h _tends_ to be first (i.e. record.c first includes
record.h, which first includes basics.h, which first includees
system.h), but not always (e.g. publicbasics.c includes another header
first that does not include system.h).  However, I'm going to punt on
making actual changes to the C files in reftable/ since I do not want to
risk bringing it out-of-sync with any version being used externally.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/sub-process.c b/sub-process.c
index 6d4232294d..1daf5a9752 100644
--- a/sub-process.c
+++ b/sub-process.c
@@ -1,6 +1,7 @@
 /*
  * Generic implementation of background process infrastructure.
  */
+#include "git-compat-util.h"
 #include "sub-process.h"
 #include "sigchain.h"
 #include "pkt-line.h"