build: Fix optimize_for_size build on Linux by adding an is_nacl guard.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 7bc43b665c4dadcd01933c9478a26aba133b3638..fa983d6aea48068c378d6e24fb2ed89c8f662e80 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1449,8 +1449,10 @@ config("optimize") {
     # Favor size over speed, /O1 must be before the common flags. The GYP
     # build also specifies /Os and /GF but these are implied by /O1.
     cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
-  } else if (optimize_for_size) {
+  } else if (optimize_for_size && !is_nacl) {
     # Favor size over speed.
+    # TODO(crbug.com/718650): Fix -Os in PNaCl compiler and remove the is_nacl
+    # guard above.
     cflags = [ "-Os" ] + common_optimize_on_cflags
   } else {
     cflags = [ "-O2" ] + common_optimize_on_cflags
@@ -1464,8 +1466,10 @@ config("optimize_no_wpo") {
     # Favor size over speed, /O1 must be before the common flags. The GYP
     # build also specifies /Os and /GF but these are implied by /O1.
     cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
-  } else if (optimize_for_size) {
+  } else if (optimize_for_size && !is_nacl) {
     # Favor size over speed.
+    # TODO(crbug.com/718650): Fix -Os in PNaCl compiler and remove the is_nacl
+    # guard above.
     cflags = [ "-Os" ] + common_optimize_on_cflags
   } else if (optimize_for_fuzzing) {
     cflags = [ "-O1" ] + common_optimize_on_cflags