[patch] fix minor typo in comment

[Jonathan Wakely]

Tested x86_64-linux, committed to trunk.

commit 176c3be1080e0b33fe02612e015e42eb2d74cf0e
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Jun 9 10:40:47 2014 +0100

    	* include/tr1/beta_function.tcc: Fix spelling of include guard in
    	comment.

diff --git a/libstdc++-v3/include/tr1/beta_function.tcc b/libstdc++-v3/include/tr1/beta_function.tcc
index c4fe6e8..e7d7c4d 100644
--- a/libstdc++-v3/include/tr1/beta_function.tcc
+++ b/libstdc++-v3/include/tr1/beta_function.tcc
@@ -194,4 +194,4 @@ namespace tr1
 }
 }
 
-#endif // __GLIBCXX_TR1_BETA_FUNCTION_TCC
+#endif // _GLIBCXX_TR1_BETA_FUNCTION_TCC