Fix building alongside other modules in nginx 1.9.11+
Fix building alongside other modules in nginx 1.9.11+

The auto/module script appends $ngx_module_libs to $CORE_LIBS itself.
Including $CORE_LIBS in $ngx_module_libs causes libraries used by any
third-party modules added prior to ngx_http_auth_pam_module to be
duplicated in the $CORE_LIBS array.

Similarly, the auto/module script appends $ngx_module_srcs to
$NGX_ADDON_SRCS (or another array, depending on the value of
$ngx_module_link) itself. Including $NGX_ADDON_SRCS in $ngx_module_srcs
ultimately cause nginx's configure script to produce a Makefile that
passes the same .o files from other third-party modules multiple times
to the linker, which causes the build to fail with duplicate symbol
errors.

This commit fixes both issues by removing $CORE_LIBS and $NGX_ADDON_SRCS
from $ngx_module_libs and $ngx_module_srcs respectively.

stogh/ngx_http_auth_pam_module