Config changes to support target_os="fuchsia"

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 151 matching lines @@
   } else if (is_android) {
     configs += [ "//build/config/android:compiler" ]
   } else if (is_linux) {
     configs += [ "//build/config/linux:compiler" ]
   } else if (is_nacl) {
     configs += [ "//build/config/nacl:compiler" ]
   } else if (is_mac) {
     configs += [ "//build/config/mac:compiler" ]
   } else if (is_ios) {
     configs += [ "//build/config/ios:compiler" ]
+  } else if (is_fuchsia) {
+    configs += [ "//build/config/fuchsia:compiler" ]
   } else if (current_os == "aix") {
     configs += [ "//build/config/aix:compiler" ]
   }
 
   # See the definitions below.
   configs += [
     ":compiler_cpu_abi",
     ":compiler_codegen",
   ]
 
@@ skipping 120 matching lines @@
         ]
         defines += [ "NO_UNWIND_TABLES" ]
       } else {
         cflags += [ "-funwind-tables" ]
       }
     }
   }
 
   # Linux/Android common flags setup.
   # ---------------------------------
-  if (is_linux || is_android) {
+  if (is_linux || is_android || is_fuchsia) {
     if (use_pic) {
       cflags += [ "-fPIC" ]
       ldflags += [ "-fPIC" ]
     }
 
     # Use pipes for communicating between sub-processes. Faster.
     cflags += [ "-pipe" ]
 
     ldflags += [
       "-Wl,-z,noexecstack",
       "-Wl,-z,now",
       "-Wl,-z,relro",
     ]
     if (!using_sanitizer) {
       if (!use_cfi_diag) {
         ldflags += [ "-Wl,-z,defs" ]
       }
 
       # Functions interposed by the sanitizers can make ld think
       # that some libraries aren't needed when they actually are,
       # http://crbug.com/234010. As workaround, disable --as-needed.
       if (!is_nacl && !is_android) {
         # TODO(pcc): Fix linker bug which requires us to link pthread
         # unconditionally here (crbug.com/623236).
         ldflags += [
           "-Wl,--no-as-needed",
           "-lpthread",
         ]
       }
-      ldflags += [ "-Wl,--as-needed" ]
+      if (!is_fuchsia) {

[jamesr1, 2017/05/11 22:00:32]

we can wrap just -lmxio with this, i.e.

ldflags += [ "-Wl,--as-needed", "-lmxio", "-Wl,--no-as-needed" ]

in the "compiler" config

+        # We need mxio/magenta to get linked in, even if they're not directly
+        # referenced.

[Nico, 2017/05/11 15:03:16]

Could you just add -l flags for those instead, to not lose --as-needed for
everything?

[scottmg, 2017/05/11 16:36:10]

Probably, yeah. Maybe what I'll do in this CL is just remove this, then in a
future CL that actually links something, it can add what it needs.

+        ldflags += [ "-Wl,--as-needed" ]
+      }
     }
   }
 
   # Linux-specific compiler flags setup.
   # ------------------------------------
   if (is_android && is_clang) {
     _rebased_android_toolchain_root =
         rebase_path(android_toolchain_root, root_build_dir)
 
     # Let clang find the linker in the NDK.
@@ skipping 1398 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }