Use GCC for snapshot_toolchain when is_clang=false.

snapshot_toolchain.gni

Index: snapshot_toolchain.gni
diff --git a/snapshot_toolchain.gni b/snapshot_toolchain.gni
index 4932110489dd1a7fe65a6124aa655192661d3bd6..4d305a9b2dcd19b8aa29bedc2bd51596556cd0c0 100644
--- a/snapshot_toolchain.gni
+++ b/snapshot_toolchain.gni
@@ -33,9 +33,17 @@
 # configurations v8 runs on.
 if (host_cpu == "x64" && host_os == "linux") {
   if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
-    snapshot_toolchain = "//build/toolchain/linux:clang_x86"
+    if (is_clang) {

[slan, 2016/03/16 17:40:05]

comment from alokp@ in Gerrit Review:

This seems equivalent to "snapshot_toolchain = host_toolchain"
https://code.google.com/p/chromium/codesearch#chromium/src/build/config/BUILD...

[slan, 2016/03/16 17:41:46]

That is what I wanted to do, but there seems to be an explicit enforcement that
x86/x64 host and target toolchain architectures are aligned.

jochen@, do you see any issue with just assigning
snapshot_toolchain=host_toolchain?

[Dirk Pranke, 2016/03/16 22:14:45]

You definitely can't use snapshot_toolchain=host_toolchain; we need to use the
32-bit x86 toolchain to maintain the same bit-width as the target 32-bit arm
toolchain (and host_toolchain is always 64-bit; we don't support 32-bit host
toolchains), otherwise the snapshot won't even work.

We did intentionally choose to always use clang for host toolchains on linux,
rather than match the compiler for the target toolchain. For android, at least,
that is an intentional choice because we want to use clang wherever possible for
linux (desktop) builds, so that we don't have to worry about supporting both gcc
and clang builds of the 64-bit tools.

Why are you making this change? Are you building in an environment where you
don't have clang for the host and snapshot toolchains?

+      snapshot_toolchain = "//build/toolchain/linux:clang_x86"
+    } else {
+      snapshot_toolchain = "//build/toolchain/linux:x86"
+    }
   } else if (target_cpu == "x64" || target_cpu == "arm64" || target_cpu == "mips64el") {
-    snapshot_toolchain = "//build/toolchain/linux:clang_x64"
+    if (is_clang) {
+      snapshot_toolchain = "//build/toolchain/linux:clang_x64"
+    } else {
+      snapshot_toolchain = "//build/toolchain/linux:x64"
+    }
   } else {
     assert(false, "Need environment for this arch: $target_cpu")
   }