Bug 1384258 - Build Stylo by default. r=chmanchester

Build Stylo (the styling system from servo) by default in all
builds for win32, win64, macOS and linux64 targets. It was
previously enabled for automation builds, so this just changes
the behaviour for local developer builds.

Note that this introduces a new dependency on libclang for the
binding generator. If you're developing on a tier-1 platform,
run `./mach boostrap` to install a working copy. Otherwise
llvm+libclang 4.0.1 is recommended.

Remove the explicit --enable-stylo=build in mozconfig.stylo
in favour of the configure default.

Add mozconfig.stylo to the hazard and debug-asan mozconfigs
so LLVM_CONFIG is defined properly for those builds.

Based on a patch by Bobby Holly in bug 1356991.

MozReview-Commit-ID: C2wRNl7JHpz

--HG--
extra : rebase_source : 1ed7c36a64e25b235a26864592cd7ea969a4cd25

browser/config/mozconfigs/linux64/debug-asan

@@ -3,6 +3,8 @@
 ac_add_options --enable-debug
 ac_add_options --enable-optimize="-O1"
 
+. $topsrcdir/build/mozconfig.stylo
+
 # ASan specific options on Linux
 ac_add_options --enable-valgrind
 

browser/config/mozconfigs/linux64/hazards

@@ -20,6 +20,8 @@ ac_add_options --enable-elf-hack
 
 . "$topsrcdir/build/unix/mozconfig.stdcxx"
 
+. "$topsrcdir/build/mozconfig.stylo"
+
 # The objdir must be at a known location so its path can be stripped from the
 # filenames stored by the analysis
 mk_add_options MOZ_OBJDIR=obj-analyzed

build/mozconfig.stylo

@@ -1,6 +1,2 @@
 # Tell the build system where to find llvm-config for builds on automation.
 export LLVM_CONFIG="${TOOLTOOL_DIR:-$topsrcdir}/clang/bin/llvm-config"
-
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build

toolkit/moz.configure

@@ -593,17 +593,27 @@ id_and_secret_keyfile('Leanplum SDK')
 option('--enable-stylo', nargs='?', choices=('build',),
        help='Include Stylo in the build and/or enable it at runtime')
 
-@depends('--enable-stylo', '--help')
-def stylo_config(value, _):
+@depends('--enable-stylo', '--help', target)
+def stylo_config(value, _, target):
     build_stylo = None
     enable_stylo = None
 
-    # The default is to not build Stylo at all.
+    # If nothing is specified, default to building stylo where possible.
     if value.origin == 'default':
-        pass
+        if target.os == 'GNU' and target.bitness == 32:
+            # The clang setup we use in automation is a little unusual, and
+            # doesn't play well with bindgen on 32-bit Linux.
+            pass
+        elif target.os == 'Android':
+            # Stylo on Android is happening Later(tm).
+            pass
+        else:
+            build_stylo = True
     elif len(value) and value[0] == 'build':
+        # Build but disable by request.
         build_stylo = True
     elif bool(value):
+        # Build and enable.
         build_stylo = True
         enable_stylo = True