zlib: fix gn error when is_clang=false target_cpu="arm"

Check use_thin_lto instead of thin_lto_enable_optimizations, as the
latter is only defined in a BUILD.gn so can't be checked outside of
it. Plus the intent of https://crrev.com/c/1642730 appears to have
been to error out on LTO in general anyway.

Fixes gn gen --args="is_clang=false target_cpu=\"arm\"" failing with:
ERROR at //third_party/zlib/BUILD.gn:105:17: Undefined identifier
        assert(!thin_lto_enable_optimizations,
                ^----------------------------

Bug: 819294
Change-Id: Ibbcae447b01043edc8a118f4a3a3923f2d0ae261
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1667663
Auto-Submit: Tomasz Śniatowski <tsniatowski@vewd.com>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#671713}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 28065982319c824cccff912f0ce561f60d054796

1 files changed, 3 insertions, 1 deletions

diff --git a/BUILD.gn b/BUILD.gn
index 3b8e5e9..64a05d1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/compiler/compiler.gni")
+
 if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
@@ -102,7 +104,7 @@ if (use_arm_neon_optimizations) {
           assert(false, "CPU detection requires the Android NDK")
         }
       } else if (!is_win && !is_clang) {
-        assert(!thin_lto_enable_optimizations,
+        assert(!use_thin_lto,
                "ThinLTO fails mixing different module-level targets")
         cflags_c = [ "-march=armv8-a+crc" ]
       }