libstdc++-v3/ChangeLog:
2009-12-22  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>

	PR libstdc++/40974
	* include/c_compatibility/fenv.h (_GLIBCXX_FENV_H):
	Turn off multiple inclusion guard for 'include_next <fenv.h>'.

diff --git a/libstdc++-v3/include/c_compatibility/fenv.h b/libstdc++-v3/include/c_compatibility/fenv.h
index 5db6d9d..ce56a95 100644
--- a/libstdc++-v3/include/c_compatibility/fenv.h
+++ b/libstdc++-v3/include/c_compatibility/fenv.h
@@ -33,7 +33,10 @@
 
 #include <bits/c++config.h>
 #if _GLIBCXX_HAVE_FENV_H
+# undef _GLIBCXX_FENV_H
 # include_next <fenv.h>
+# undef _GLIBCXX_FENV_H
+# define _GLIBCXX_FENV_H 1
 #endif
 
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
