Remove usage of __register_atfork

Calling an internal function of glibc is never a good idea.
This is especially true for __register_atfork which is not defined on
uClibc with noMMU.
So remove call to __register_atfork and so always use pthread_atfork

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
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test

00:00:58

 
Name Stage Failure
failed
test Test
Makefile:735: recipe for target 'overlay' failed
make[2]: *** [overlay] Error 1
make[2]: Leaving directory '/builds/ffontaine/libbsd/test'
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make[1]: *** [check-am] Error 2
make[1]: Leaving directory '/builds/ffontaine/libbsd/test'
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make: *** [check-recursive] Error 1
ERROR: Job failed: exit code 1