btrfs: introduce EXPORT_FOR_TESTS macro

Depending on whether CONFIG_BTRFS_FS_RUN_SANITY_TESTS is set, some BTRFS
functions are either local to the file they are implemented in and thus
should be declared static or are called from within the test
implementation defined in a different file.

Introduce an EXPORT_FOR_TESTS macro which depending on
CONFIG_BTRFS_FS_RUN_SANITY_TESTS either adds the 'static' keyword to a
function or not.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3471,6 +3471,16 @@ static inline void assfail(const char *expr, const char *file, int line)
 #define ASSERT(expr)	((void)0)
 #endif
 
+/*
+ * Use that for functions that are conditionally exported for sanity tests but
+ * otherwise static
+ */
+#ifndef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+#define EXPORT_FOR_TESTS static
+#else
+#define EXPORT_FOR_TESTS
+#endif
+
 __cold
 static inline void btrfs_print_v0_err(struct btrfs_fs_info *fs_info)
 {