Rework approach to allowing extra flags for CrOS builds.

build/toolchain/cros/BUILD.gn

Index: build/toolchain/cros/BUILD.gn
diff --git a/build/toolchain/cros/BUILD.gn b/build/toolchain/cros/BUILD.gn
index bf139dc12da8192f02bd1e7c83e18c3a77f795a5..999a22b0509cbdd30f974c4c68a0b1b0b2cdf7e6 100644
--- a/build/toolchain/cros/BUILD.gn
+++ b/build/toolchain/cros/BUILD.gn
@@ -22,10 +22,6 @@ gcc_toolchain("target") {
   if (cros_target_readelf != "") {
     readelf = cros_target_readelf
   }
-  extra_cflags = cros_target_extra_cflags
-  extra_cppflags = cros_target_extra_cppflags
-  extra_cxxflags = cros_target_extra_cxxflags
-  extra_ldflags = cros_target_extra_ldflags
 
   toolchain_args = {
     cc_wrapper = ""
@@ -56,10 +52,6 @@ gcc_toolchain("nacl_bootstrap") {
   if (cros_target_readelf != "") {
     readelf = cros_target_readelf
   }
-  extra_cflags = cros_nacl_bootstrap_extra_cflags
-  extra_cppflags = cros_nacl_bootstrap_extra_cppflags
-  extra_cxxflags = cros_nacl_bootstrap_extra_cxxflags
-  extra_ldflags = cros_nacl_bootstrap_extra_ldflags
 
   toolchain_args = {
     cc_wrapper = ""
@@ -87,10 +79,6 @@ gcc_toolchain("host") {
   if (cros_host_readelf != "") {
     readelf = cros_host_readelf
   }
-  extra_cflags = cros_host_extra_cflags
-  extra_cppflags = cros_host_extra_cppflags
-  extra_cxxflags = cros_host_extra_cxxflags
-  extra_ldflags = cros_host_extra_ldflags
 
   toolchain_args = {
     cc_wrapper = ""
@@ -116,10 +104,6 @@ gcc_toolchain("v8_snapshot") {
   if (cros_v8_snapshot_readelf != "") {
     readelf = cros_v8_snapshot_readelf
   }
-  extra_cflags = cros_v8_snapshot_extra_cflags
-  extra_cppflags = cros_v8_snapshot_extra_cppflags
-  extra_cxxflags = cros_v8_snapshot_extra_cxxflags
-  extra_ldflags = cros_v8_snapshot_extra_ldflags
 
   toolchain_args = {
     cc_wrapper = ""