glibc: replace extern __inline with __extern_inline.

* this helps to comply with C99. As a reminder, some of these headers
are also used by x86_gcc2 src/libs/stdc++.

Renamed src/kernel to src/system.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12359 a95241bf-73f2-0310-859d-f6bbb57e9c96

Merge branch 'master' into app_server