IWYU widely useful pragmas

Add various widely useful "IWYU pragma" annotations, such as

- Common header files such as c.h, postgres.h should be "always_keep".

- System headers included in c.h, postgres.h etc. should be considered
  "export".

- Some portability headers such as getopt_long.h should be
  "always_keep", so they are not considered superfluous on some
  platforms.

- Certain system headers included from portability headers should be
  considered "export" because the purpose of the portability header is
  to wrap them.

- Superfluous includes marked as "for backward compatibility" get a
  formal IWYU annotation.

- Generated header included in utils/syscache.h is marked exported.
  This is a very commonly used include and this avoids lots of
  complaints.

Discussion: https://www.postgresql.org/message-id/flat/[email protected]

1 files changed, 3 insertions, 2 deletions

diff --git a/src/include/pg_getopt.h b/src/include/pg_getopt.h
index 2e2d64f4a26..aad0886c054 100644
--- a/src/include/pg_getopt.h
+++ b/src/include/pg_getopt.h
@@ -15,15 +15,16 @@
  *
  * src/include/pg_getopt.h
  */
+/* IWYU pragma: always_keep */
 #ifndef PG_GETOPT_H
 #define PG_GETOPT_H
 
 /* POSIX says getopt() is provided by unistd.h */
-#include <unistd.h>
+#include <unistd.h>				/* IWYU pragma: export */
 
 /* rely on the system's getopt.h if present */
 #ifdef HAVE_GETOPT_H
-#include <getopt.h>
+#include <getopt.h>				/* IWYU pragma: export */
 #endif
 
 /*