picom: misc fixes

- Build option `build_docs` was renamed to `with_docs` quite sometime ago:
  3f2a6718df.
  This means that the manpage were not being build.
- Remove CFLAG `-fno-strict-aliasing` seems to not be used anywhere in the
  upstream repository. This was probably added for `compton` a long time
  ago and never removed, since I can't find the commit that added this.
- Use release build. This is recommended upstream:
  https://github.com/yshui/picom#to-build.

pkgs/applications/window-managers/picom/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchFromGitHub, pkgconfig, uthash, asciidoc, docbook_xml_dtd_45
+{ stdenv, lib, fetchFromGitHub, pkg-config, uthash, asciidoc, docbook_xml_dtd_45
 , docbook_xsl, libxslt, libxml2, makeWrapper, meson, ninja
 , xorgproto, libxcb ,xcbutilrenderutil, xcbutilimage, pixman, libev
 , dbus, libconfig, libdrm, libGL, pcre, libX11
@@ -18,7 +18,7 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [
     meson ninja
-    pkgconfig
+    pkg-config
     uthash
     asciidoc
     docbook_xml_dtd_45
@@ -35,10 +35,10 @@ stdenv.mkDerivation rec {
     libxdg_basedir
   ];
 
-  NIX_CFLAGS_COMPILE = "-fno-strict-aliasing";
+  mesonBuildType = "release";
 
   mesonFlags = [
-    "-Dbuild_docs=true"
+    "-Dwith_docs=true"
   ];
 
   installFlags = [ "PREFIX=$(out)" ];