GN: Use x86_64-nacl-gcc with -m32 rather then i686-nacl-gcc

build/toolchain/nacl/BUILD.gn

Index: build/toolchain/nacl/BUILD.gn
diff --git a/build/toolchain/nacl/BUILD.gn b/build/toolchain/nacl/BUILD.gn
index 3896e1964d4a55492ca41791acc66887282048f0..5cbfc008fe55562a82e5c74f1d69e230f84ac1ef 100644
--- a/build/toolchain/nacl/BUILD.gn
+++ b/build/toolchain/nacl/BUILD.gn
@@ -106,6 +106,7 @@ pnacl_toolchain("newlib_pnacl_nonsfi") {
 
 template("nacl_glibc_toolchain") {
   toolchain_cpu = target_name
+  toolchain_cc_args = ""
   assert(defined(invoker.toolchain_tuple), "Must define toolchain_tuple")
   assert(defined(invoker.toolchain_package), "Must define toolchain_package")
   assert(defined(invoker.toolchain_revision), "Must define toolchain_revision")
@@ -113,6 +114,7 @@ template("nacl_glibc_toolchain") {
                          [
                            "toolchain_package",
                            "toolchain_revision",
+                           "toolchain_cc_args",
                          ])
 
   toolprefix = rebase_path("${nacl_toolchain_dir}/${toolchain_package}/bin/" +
@@ -131,8 +133,8 @@ template("nacl_glibc_toolchain") {
     is_clang = false
     is_nacl_glibc = true
 
-    cc = toolprefix + "gcc" + toolsuffix
-    cxx = toolprefix + "g++" + toolsuffix
+    cc = toolprefix + "gcc" + toolsuffix + toolchain_cc_args
+    cxx = toolprefix + "g++" + toolsuffix + toolchain_cc_args
     ar = toolprefix + "ar" + toolsuffix
     ld = cxx
     readelf = toolprefix + "readelf" + toolsuffix
@@ -144,7 +146,11 @@ template("nacl_glibc_toolchain") {
 nacl_glibc_toolchain("x86") {
   toolchain_package = "nacl_x86_glibc"
   toolchain_revision = nacl_x86_glibc_rev
-  toolchain_tuple = "i686-nacl"
+
+  # i686-nacl-gcc is not in goma (adding it would be tricky) so we use
+  # x86_64-nacl compiler with the -m32 flags.
+  toolchain_tuple = "x86_64-nacl"
+  toolchain_cc_args = " -m32"
 }
 
 nacl_glibc_toolchain("x64") {