Without that commit the macro __extern_inline can be used without being defined:


$ cat test.cpp
#include <fenv.h>
$ /usr/bin/clang++ -c test.cpp  -O
In file included from test.cpp:1:
In file included from /usr/include/fenv.h:58:
/usr/include/bits/fenv.h:105:1: error: unknown type name '__extern_inline'
__extern_inline int
^
/usr/include/bits/fenv.h:105:17: error: expected unqualified-id
__extern_inline int
                ^
2 errors generated.