Use GN subconfigs for Android, optimization, and symbols.

build/config/android/BUILD.gn

Index: build/config/android/BUILD.gn
diff --git a/build/config/android/BUILD.gn b/build/config/android/BUILD.gn
index 5492693f560fc02885b96524070503f9e7f0cf07..6f9258f8d8043aca0f68764131b94bfa38c48e1b 100644
--- a/build/config/android/BUILD.gn
+++ b/build/config/android/BUILD.gn
@@ -3,8 +3,11 @@
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
+import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/sysroot.gni")
 
+assert(is_android)
+
 config("sdk") {
   if (sysroot != "") {
     cflags = [ "--sysroot=" + sysroot ]
@@ -30,3 +33,112 @@ config("hide_native_jni_exports") {
   ldflags = [ "-Wl,--version-script=" +
               rebase_path("//build/android/android_no_jni_exports.lst") ]
 }
+
+# This is included by reference in the //build/config/compiler config that
+# is applied to all targets. It is here to separate out the logic that is
+# Android-only.
+config("compiler") {
+  cflags = [
+    "-ffunction-sections",
+    "-funwind-tables",
+    "-fno-short-enums",
+  ]
+  defines = [
+    "ANDROID",
+
+    # The NDK has these things, but doesn't define the constants to say that it
+    # does. Define them here instead.
+    "HAVE_SYS_UIO_H",
+  ]
+  ldflags = []
+
+  if (!is_clang) {
+    # Clang doesn't support these flags.
+    cflags += [ "-finline-limit=64" ]
+  }
+  if (is_clang) {
+    rebased_android_toolchain_root =
+        rebase_path(android_toolchain_root, root_build_dir)
+    if (current_cpu == "arm") {
+      cflags += [
+        # TODO(hans) Enable integrated-as (crbug.com/124610).
+        "-no-integrated-as",
+        "-B${rebased_android_toolchain_root}/bin",  # Else /usr/bin/as gets picked up.
+      ]
+    }
+  }
+
+  if (is_asan) {
+    # Android build relies on -Wl,--gc-sections removing unreachable code.
+    # ASan instrumentation for globals inhibits this and results in a library
+    # with unresolvable relocations.
+    # TODO(eugenis): find a way to reenable this.
+    cflags += [ "-mllvm -asan-globals=0" ]
+  }
+
+  # Use gold for Android for most CPU architectures.
+  if (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm") {
+    ldflags += [ "-fuse-ld=gold" ]
+    if (is_clang) {
+      # Let clang find the ld.gold in the NDK.
+      ldflags += [ "--gcc-toolchain=$rebased_android_toolchain_root" ]
+    }
+
+    # Use -mstackrealign due to a bug on ia32 Jelly Bean.
+    # See crbug.com/521527
+    if (current_cpu == "x86") {
+      cflags += [ "-mstackrealign" ]
+    }
+  }
+
+  ldflags += [
+    "-Wl,--no-undefined",
+
+    # Don't allow visible symbols from libgcc or libc++ to be
+    # re-exported.
+    "-Wl,--exclude-libs=libgcc.a",
+    "-Wl,--exclude-libs=libc++_static.a",
+
+    # Don't allow visible symbols from libraries that contain
+    # assembly code with symbols that aren't hidden properly.
+    # http://crbug.com/448386
+    "-Wl,--exclude-libs=libvpx_assembly_arm.a",
+  ]
+  if (current_cpu == "arm") {
+    ldflags += [
+      # Enable identical code folding to reduce size.
+      "-Wl,--icf=safe",
+    ]
+  }
+
+  if (is_clang) {
+    if (current_cpu == "arm") {
+      abi_target = "arm-linux-androideabi"
+    } else if (current_cpu == "x86") {
+      abi_target = "i686-linux-androideabi"
+    } else if (current_cpu == "arm64") {
+      # Place holder for arm64 support, not tested.
+      abi_target = "aarch64-linux-androideabi"
+    } else if (current_cpu == "x64") {
+      # Place holder for x64 support, not tested.
+      # TODO: Enable clang support for Android x64. http://crbug.com/346626
+      abi_target = "x86_64-linux-androideabi"
+    } else if (current_cpu == "mipsel") {
+      # Place holder for mips support, not tested.
+      abi_target = "mipsel-linux-androideabi"
+    } else if (current_cpu == "mips64el") {
+      # Place holder for mips64 support, not tested.
+      abi_target = "mips64el-linux-androideabi"
+    } else {
+      assert(false, "Architecture not supported")
+    }
+    cflags += [
+      "-target",
+      abi_target,
+    ]
+    ldflags += [
+      "-target",
+      abi_target,
+    ]
+  }
+}