Remove pragma weak for undeclared symbol

pthread_initialize is a static function and should not be mentioned in a
header.  The #pragma weak for it appears to confuse gcc-4.7.

see gcc PR middle-end/36282

Signed-off-by: Bernd Schmidt <bernds@codesourcery.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>