Add new system view, pg_config

Move and refactor the underlying code for the pg_config client
application to src/common in support of sharing it with a new
system information SRF called pg_config() which makes the same
information available via SQL. Additionally wrap the SRF with a
new system view, as called pg_config.

Patch by me with extensive input and review by Michael Paquier
and additional review by Alvaro Herrera.

src/common/config_info.c

@@ -0,0 +1,206 @@
+/*-------------------------------------------------------------------------
+ *
+ * config_info.c
+ *		Common code for pg_config output
+ *
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/common/config_info.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include "miscadmin.h"
+#include "common/config_info.h"
+
+static size_t configdata_names_len(void);
+
+static const char *const configdata_names[] =
+{
+	"BINDIR",
+	"DOCDIR",
+	"HTMLDIR",
+	"INCLUDEDIR",
+	"PKGINCLUDEDIR",
+	"INCLUDEDIR-SERVER",
+	"LIBDIR",
+	"PKGLIBDIR",
+	"LOCALEDIR",
+	"MANDIR",
+	"SHAREDIR",
+	"SYSCONFDIR",
+	"PGXS",
+	"CONFIGURE",
+	"CC",
+	"CPPFLAGS",
+	"CFLAGS",
+	"CFLAGS_SL",
+	"LDFLAGS",
+	"LDFLAGS_EX",
+	"LDFLAGS_SL",
+	"LIBS",
+	"VERSION",
+	NULL
+};
+
+static size_t
+configdata_names_len(void)
+{
+	size_t	i = 0;
+
+	while (configdata_names[i])
+		i++;
+
+	return i;
+}
+
+/*
+ * get_configdata(char *my_exec_path, size_t *configdata_len)
+ *
+ * Get configure-time constants. The caller is responsible
+ * for pfreeing the result.
+ */
+ConfigData *
+get_configdata(char *my_exec_path, size_t *configdata_len)
+{
+	ConfigData	   *configdata;
+	char			path[MAXPGPATH];
+	char		   *lastsep;
+	int				i;
+
+	*configdata_len = configdata_names_len();
+	configdata = palloc(*configdata_len * sizeof(ConfigData));
+
+	/*
+	 * initialize configdata names
+	 *
+	 * These better be in sync with the settings manually
+	 * defined below.
+	 */
+	for (i = 0; i < *configdata_len; i++)
+		configdata[i].name = pstrdup(configdata_names[i]);
+
+	strcpy(path, my_exec_path);
+	lastsep = strrchr(path, '/');
+	if (lastsep)
+		*lastsep = '\0';
+	cleanup_path(path);
+	configdata[0].setting = pstrdup(path);
+
+	get_doc_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[1].setting = pstrdup(path);
+
+	get_html_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[2].setting = pstrdup(path);
+
+	get_include_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[3].setting = pstrdup(path);
+
+	get_pkginclude_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[4].setting = pstrdup(path);
+
+	get_includeserver_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[5].setting = pstrdup(path);
+
+	get_lib_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[6].setting = pstrdup(path);
+
+	get_pkglib_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[7].setting = pstrdup(path);
+
+	get_locale_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[8].setting = pstrdup(path);
+
+	get_man_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[9].setting = pstrdup(path);
+
+	get_share_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[10].setting = pstrdup(path);
+
+	get_etc_path(my_exec_path, path);
+	cleanup_path(path);
+	configdata[11].setting = pstrdup(path);
+
+	get_pkglib_path(my_exec_path, path);
+	strlcat(path, "/pgxs/src/makefiles/pgxs.mk", sizeof(path));
+	cleanup_path(path);
+	configdata[12].setting = pstrdup(path);
+
+#ifdef VAL_CONFIGURE
+	configdata[13].setting = pstrdup(VAL_CONFIGURE);
+#else
+	configdata[13].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_CC
+	configdata[14].setting = pstrdup(VAL_CC);
+#else
+	configdata[14].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_CPPFLAGS
+	configdata[15].setting = pstrdup(VAL_CPPFLAGS);
+#else
+	configdata[15].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_CFLAGS
+	configdata[16].setting = pstrdup(VAL_CFLAGS);
+#else
+	configdata[16].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_CFLAGS_SL
+	configdata[17].setting = pstrdup(VAL_CFLAGS_SL);
+#else
+	configdata[17].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_LDFLAGS
+	configdata[18].setting = pstrdup(VAL_LDFLAGS);
+#else
+	configdata[18].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_LDFLAGS_EX
+	configdata[19].setting = pstrdup(VAL_LDFLAGS_EX);
+#else
+	configdata[19].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_LDFLAGS_SL
+	configdata[20].setting = pstrdup(VAL_LDFLAGS_SL);
+#else
+	configdata[20].setting = pstrdup(_("not recorded"));
+#endif
+
+#ifdef VAL_LIBS
+	configdata[21].setting = pstrdup(VAL_LIBS);
+#else
+	configdata[21].setting = pstrdup(_("not recorded"));
+#endif
+
+	configdata[22].setting = pstrdup("PostgreSQL " PG_VERSION);
+
+	return configdata;
+}