nginx: fixed building as a dynamic module

[defanator]

Building passenger using the "--add-dynamic-module" configure option in nginx >= 1.9.11 leads to linking errors like the following one:

/usr/bin/ld: /home/defan/src/nginx-1.9.12/passenger-5.0.26/buildout/common/libpassenger_common/Logging.o: relocation R_X86_64_32 against `.bss' can not be used when making a shared object; recompile with -fPIC
/home/defan/src/nginx-1.9.12/passenger-5.0.26/buildout/common/libpassenger_common/Logging.o: could not read symbols: Bad value
collect2: ld returned 1 exit status
make[1]: *** [objs/ngx_http_passenger_module.so] Error 1
make[1]: Leaving directory `/home/defan/src/nginx-1.9.12'
make: *** [build] Error 2

The proposed patch adds "-fPIC" as a global EXTRA_CXXFLAGS variable that is being used later by rake.

Tested with nginx/1.9.12 + Passenger 5.0.26 on CentOS 6.7.

[FooBarWidget]

Whoops, I only tested on OS X and missed that.

[OnixGH]

There are some issues with this patch:

• EXTRA_CXXFLAGS makes the agent itself get compiled with -fPIC, which it shouldn't be
• If objects were already compiled (with some other flags) this will not recompile them

Suggested improvements:

• Add rake nginx:dynamic_module_dependencies task that compiles just the .o dependencies of the nginx module with -fPIC (to another build output dir)
• Nginx config script executes rake nginx as well as rake nginx:dynamic_module_dependencies when passenger is configured as a dynamic module
• Nginx config script that normally links to the static .o files should link to the dynamic .o files when passenger is configured as dynamic module (generated by rake nginx:dynamic_module_dependencies)

[OnixGH]

Copied to https://github.com/phusion/passenger/tree/defanator-nginx_fix_dynamic_build to work on fixing it.