This patch allows us to use LLVM's gold linker on Linux.

This patch partly reverts https://chromium.googlesource.com/chromium/src.git/+/0f268cb3af337cf608bd1902148a84195837ad1b%5E%21/
Also see https://bugs.chromium.org/p/chromium/issues/detail?id=607968 around comment №100.
I did not understand why the gold linker was disallowed on Linux, it was allowed beforehand.

After commit https://chromium.googlesource.com/chromium/src/+/dd160677bc6cd8a5ab468c187f61902a8fbf4b41%5E%21
use_lld was forced to True on x86_64 even if use_gold was True. On i586 gold was used correctly. Trying to workaround it.

this patch temporarily breaks building with use+ldd=true because it forces use_ldd=false and use_gold=true.

Author: Mikhail Novosyolov <m.novosyolov@rosalinux.ru>
--- a/build/config/compiler/BUILD.gn	2018-10-20 12:45:09.760295019 +0300
+++ b/build/config/compiler/BUILD.gn	2018-10-20 12:51:07.536125696 +0300
@@ -588,8 +588,7 @@
   # TODO(pcc): Make this conditional on is_official_build rather than on gn
   # flags for specific features.
   if (!is_debug && use_thin_lto && current_toolchain == default_toolchain) {
-    assert(use_lld || target_os == "chromeos",
-           "gold plugin only supported with ChromeOS")
+    assert(use_lld, "gold plugin cannot be used with lld linker")
 
     cflags += [ "-flto=thin" ]
 
--- a/build/config/compiler/compiler.gni     2018-10-21 02:15:50.290369454 +0300
+++ b/build/config/compiler/compiler.gni  2018-10-21 12:38:18.521273343 +0300
@@ -63,6 +63,12 @@
   # It's currently not possible to collect AFDO profiles on anything but
   # x86{,_64}.
   using_mismatched_sample_profile = current_cpu != "x64" && current_cpu != "x86"
+  
+  # ROSA-allow-Gold-on-Linux.patch patches out some code for setting these variables,
+  # so we have to set them manually
+  use_lld = false
+  use_gold = true
+  
 }
 
 assert(!is_cfi || use_thin_lto, "CFI requires ThinLTO")
@@ -157,30 +163,6 @@
   }
 }
 
-declare_args() {
-  # Set to true to use lld, the LLVM linker. This flag may be used on Windows,
-  # Linux or Fuchsia.
-  # TODO(pcc): Enable lld on more architectures on Linux. E.g. we probably need
-  # to fix some of crbug.com/742655 to enable it on ARM.
-  use_lld =
-      is_clang &&
-      (is_win || is_fuchsia || (use_thin_lto && target_os != "chromeos") ||
-       (is_linux && current_cpu == "x64" && target_os != "chromeos") ||
-       (is_android && (current_cpu != "arm" || arm_version >= 7) &&
-        current_cpu != "mipsel" && current_cpu != "mips64el"))
-}
-
-declare_args() {
-  # Whether to use the gold linker from binutils instead of lld or bfd.
-  use_gold = !use_lld && !(is_chromecast && is_linux &&
-                           (current_cpu == "arm" || current_cpu == "mipsel")) &&
-             ((is_linux && (current_cpu == "x64" || current_cpu == "x86" ||
-                            current_cpu == "arm" || current_cpu == "mipsel" ||
-                            current_cpu == "mips64el")) ||
-              (is_android && (current_cpu == "x86" || current_cpu == "x64" ||
-                              current_cpu == "arm" || current_cpu == "arm64")))
-}
-
 # If it wasn't manually set, set to an appropriate default.
 assert(symbol_level >= -1 && symbol_level <= 2, "Invalid symbol_level")
 if (symbol_level == -1) {

--- a/build/config/compiler/BUILD.gn 2018-10-21 01:41:30.065502783 +0300
+++ b/build/config/compiler/BUILD.gn      2018-10-21 21:33:10.465382423 +0300
@@ -588,8 +588,6 @@
   # TODO(pcc): Make this conditional on is_official_build rather than on gn
   # flags for specific features.
   if (!is_debug && use_thin_lto && current_toolchain == default_toolchain) {
-    assert(use_lld, "gold plugin cannot be used with lld linker")
-
     cflags += [ "-flto=thin" ]
 
     # Limit the size of the ThinLTO cache to the lesser of 10% of available disk