[libsecret] Fix -Wunknown-pragmas triggered by secret-version.h

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 2b4adfb9f429767f4ad4b2b624486d7c33f9fa55
Author: Michael Catanzaro <mcatanzaro posteo net>
Date:   Thu Jun 13 15:00:20 2019 +0000

    Fix -Wunknown-pragmas triggered by secret-version.h
    
    In file included from /usr/include/libsecret-1/libsecret/secret.h:33,
                     from ../lib/sync/../ephy-sync-utils.h:24,
                     from ../lib/sync/ephy-history-manager.c:25:
    /usr/include/libsecret-1/libsecret/secret-version.h:19: error: ignoring #pragma __once__  
[-Werror=unknown-pragmas]
     #pragma __once__
    
    It should be #pragma once, not #pragma __once__.
    
    But let's follow the other public headers here instead.

 libsecret/secret-version.h.in | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/libsecret/secret-version.h.in b/libsecret/secret-version.h.in
index 30a8389..6b777e9 100644
--- a/libsecret/secret-version.h.in
+++ b/libsecret/secret-version.h.in
@@ -16,7 +16,8 @@
 #error "Only <libsecret/secret.h> can be included directly."
 #endif
 
-#pragma __once__
+#ifndef __SECRET_VERSION_H__
+#define __SECRET_VERSION_H__
 
 /**
  * SECTION:secret-version
@@ -63,3 +64,5 @@
      (SECRET_MAJOR_VERSION == (major) &&                \
       SECRET_MINOR_VERSION == (minor) &&                \
       SECRET_MICRO_VERSION >= (micro)))
+
+#endif __SECRET_VERSION_H__