Use plain ‘static’ for Emacs C inline functions

This improved performance of ‘make compile-always’ by 8.2%
on my platform (AMD Phenom II X4 910e, Fedora 30 x86-64).
* src/conf_post.h (INLINE, EXTERN_INLINE, INLINE_HEADER_BEGIN)
(INLINE_HEADER_END) [!EMACS_EXTERN_INLINE]: Use plain ‘static’.
1 job for master in 53 minutes and 36 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #3206
test-all

00:53:36

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1