Use clang for snapshot_toolchain by default, except on ChromeOS.

snapshot_toolchain.gni

 # Copyright 2015 the V8 project authors. All rights reserved.
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 # modification, are permitted provided that the following conditions are
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 #     * Redistributions in binary form must reproduce the above
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 #       with the distribution.
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 #       from this software without specific prior written permission.
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+import("//build/config/chromecast_build.gni")

[jochen (gone - plz use gerrit), 2016/08/22 15:46:53]

why is that required here?

[slan, 2016/08/22 15:54:25]

is_chromecast is declared in that file. 

[jochen (gone - plz use gerrit), 2016/08/22 15:57:46]

but we also don't include special files to get the definition of is_android

 import("//build/config/v8_target_cpu.gni")
 
 declare_args() {
   # The v8 snapshot needs to be built by code that is compiled with a
   # toolchain that matches the bit-width of the target CPU, but runs on
   # the host.
   v8_snapshot_toolchain = ""
 }
 
 # Try to infer the appropriate snapshot toolchain for the v8_current_cpu
@@ skipping 27 matching lines @@
 
   } else if (current_os == "win" && host_os == "mac" && is_clang) {
     # This is a mac -> win cross-compile, which is only supported w/ clang.
     v8_snapshot_toolchain = "//build/toolchain/mac:clang_${v8_current_cpu}"
 
   } else if (host_cpu == "x64") {
     # This is a cross-compile from an x64 host to either a non-Intel target
     # cpu or a different target OS. Assume the same toolchain (Clang or GCC
     # or MSVS) for target and host, unless this is an Android build, where
     # Clang is always used on the host.
-    if (is_clang || is_android) {
+    if (is_clang || is_android || is_chromecast) {
       _clang = "clang_"
     } else {
       _clang = ""
     }
 
     if (v8_current_cpu == "x64" || v8_current_cpu == "x86") {
       _cpus = v8_current_cpu
     } else if (v8_current_cpu == "arm64" || v8_current_cpu == "mips64el") {
       _cpus = "x64_v8_${v8_current_cpu}"
     } else if (v8_current_cpu == "arm" || v8_current_cpu == "mipsel") {
       _cpus = "x86_v8_${v8_current_cpu}"
     } else {
       # This branch should not be reached; leave _cpus blank so the assert
       # below will fail.
       _cpus = ""
     }
 
     if (_cpus != "") {
       v8_snapshot_toolchain = "//build/toolchain/${host_os}:${_clang}${_cpus}"
     }
   }
 }
 
 assert(v8_snapshot_toolchain != "",
        "Do not know how to build a snapshot for $current_toolchain " +
        "on $host_os $host_cpu")