Revert of Change v8_snapshot_toolchain to be a GN build arg. (patchset #3...

Revert of Change v8_snapshot_toolchain to be a GN build arg. (patchset #3 id:40001 of https://codereview.chromium.org/1969693002/ )

Reason for revert:
Blocks the roll: https://codereview.chromium.org/1974733002/

Breaks:
https://build.chromium.org/p/tryserver.chromium.linux/builders/chromeos_daisy_chromium_compile_only_ng/builds/136166

Original issue's description:
> Change v8_snapshot_toolchain to be a GN build arg.
>
> It is likely that CrOS and other distros will want to be
> able to build the v8 snapshot with a custom toolchain.
>
> This CL makes snapshot_toolchain a declared build arg, and
> renames it to v8_snapshot_toolchain to minimize the risk
> of a name collision.
>
> R=machenbach@chromium.org, jochen@chromium.org
> BUG=608596
>
> Committed: https://crrev.com/2ae74af8f405f461d8e44d60b978f940673e46c8
> Cr-Commit-Position: refs/heads/master@{#36193}

TBR=jochen@chromium.org,dpranke@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=608596

Review-Url: https://codereview.chromium.org/1975713002
Cr-Commit-Position: refs/heads/master@{#36199}

snapshot_toolchain.gni

@@ -25,40 +25,22 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-declare_args() {
-  # The snapshot needs to be compiled for the host, but compiled with
-  # a toolchain that matches the bit-width of the target.
-  v8_snapshot_toolchain = ""
-}
+# The snapshot needs to be compiled for the host, but compiled with
+# a toolchain that matches the bit-width of the target.
 
 # TODO(GYP): For now we only support 32-bit little-endian target builds from an
 # x64 Linux host. Eventually we need to support all of the host/target
 # configurations v8 runs on.
-if (v8_snapshot_toolchain == "") {
-  if (host_cpu == "x64" && host_os == "linux") {
-    if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
-      if (target_os == "android" || is_clang) {
-        v8_snapshot_toolchain = "//build/toolchain/linux:clang_x86"
-      } else {
-        v8_snapshot_toolchain = "//build/toolchain/linux:x86"
-      }
-
-    } else if (target_cpu == "x64" || target_cpu == "arm64" ||
-               target_cpu == "mips64el") {
-      if (target_os == "android" || is_clang) {
-        v8_snapshot_toolchain = "//build/toolchain/linux:clang_x64"
-      } else {
-        v8_snapshot_toolchain = "//build/toolchain/linux:x64"
-      }
-    } else {
-      assert(false, "Need environment for this arch: $target_cpu")
-    }
+if (host_cpu == "x64" && host_os == "linux") {
+  if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x86"
+  } else if (target_cpu == "x64" || target_cpu == "arm64" || target_cpu == "mips64el") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x64"
   } else {
-    v8_snapshot_toolchain = default_toolchain
+    assert(false, "Need environment for this arch: $target_cpu")
   }
+} else {
+  snapshot_toolchain = default_toolchain
 }
 
-# TODO(GYP): snapshot_toolchain is provided for backwards compatibility
-# and should be removed once all callers are updated to refer to
-# v8_snapshot_toolchain directly.
-snapshot_toolchain = v8_snapshot_toolchain
+