Compile host specific files when cross-compiling

This fixes Chromium (mips64el) cross-comile failure
for v8 snapshot for host.

Bug: b/115344057, b/117854176
Change-Id: I0a348701151b9db288a3de84ef22c23bbd007a80
Reviewed-on: https://swiftshader-review.googlesource.com/c/22408
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Milko Leporis <milko.leporis@mips.com>
diff --git a/third_party/llvm-7.0/BUILD.gn b/third_party/llvm-7.0/BUILD.gn
index a91bbcd..744b0eb 100644
--- a/third_party/llvm-7.0/BUILD.gn
+++ b/third_party/llvm-7.0/BUILD.gn
@@ -405,6 +405,11 @@
   } else {
     assert(false, "Unsupported target_cpu")
   }
+
+  if (target_cpu != current_cpu &&
+      (current_cpu == "x86" || current_cpu == "x64")) {
+    deps += [ ":swiftshader_llvm_x86" ]
+  }
 }
 
 swiftshader_source_set("swiftshader_llvm_x86") {