* lib/thread-optim.h: Include <stdbool.h>.
(gl_multithreaded): Define differently on ELF platforms.
(_GL_MULTITHREADED_ALWAYS_TRUE, _GL_MULTITHREADED_VIA_ELF): New macros.
(gl_set_multithreaded): New declaration.
* lib/thread-optim.c: New file.
* lib/thread-creators.gperf: New file.
* lib/thread-optim-proto.c: New file.
* modules/thread-optim (Files): Add these files.
(Depends-on): Add gperf, bool, stdint-h.
(configure.ac): Test for <link.h>, dl_iterate_phdr.
(Makefile.am): Compile thread-optim.c. Create thread-creators.h through
gperf.
tweak