Support building ngx_pagespeed as a dynamic module

[oschaaf]

As of 1.9.11, nginx supports loading dynamic modules
This change makes us support building ngx_pagespeed.so

Fixes #1116

[PiotrSikora]

This looks very wrong to me, this patch:

1. always compilies both modules as static modules, even when compiling as a dynamic modules (using --add-dynamic-module),
2. misuses ngx_module_order, which doesn't work with filters running after current filter, only earlier ones.

See: google/ngx_brotli@86998c6

[oschaaf]

@PiotrSikora Updated and force pushed. This will need to be rebased, but does this look better?

[PiotrSikora]

@oschaaf: looks good, but it seems that you also need to modify config.make in order to pass --std=c++11 when compiling with clang, otherwise it doesn't build.

Also, ngx_http_brotli_filter_module and ngx_http_gzip_filter_module should switch places.

[oschaaf]

@PiotrSikora config.make is not executed for dynamic modules, see https://github.com/nginx/nginx/blob/master/auto/make#L436

So this is the best I can come up with to allow us to build ngx_pagespeed.so with clang

[oschaaf]

@PiotrSikora Comments addressed & force pushed

[PiotrSikora]

Style: this module uses $(...) for shell commands, so we should be consistent about it.

[PiotrSikora]

@oschaaf: thanks, LGTM (other than the stuff that I commented on, which can be mostly ignored).

[oschaaf]

@PiotrSikora Thanks for reviewing! I updated to address your latest comments.

[crowell]

@oschaaf is this ready to merge?

[oschaaf]

@crowell yes

[crowell]

LGTM, backported and tested on master.