diff --git a/config/c++/c++.gni b/config/c++/c++.gni
index 5ced4596f..db1b27cb2 100644
--- a/config/c++/c++.gni
+++ b/config/c++/c++.gni
@@ -11,7 +11,7 @@ declare_args() {
   # Don't check in changes that set this to false for more platforms; doing so
   # is not supported.
   use_custom_libcxx =
-      is_fuchsia || is_android || is_mac || (is_ios && !use_xcode_clang) ||
+      is_fuchsia || is_android || (is_mac && !use_xcode_clang) || (is_ios && !use_xcode_clang) ||
       (is_win && is_clang) ||
       (is_linux &&
        (!is_chromeos || default_toolchain != "//build/toolchain/cros:target"))
diff --git a/config/compiler/BUILD.gn b/config/compiler/BUILD.gn
index 3d5e4dede..99b06680c 100644
--- a/config/compiler/BUILD.gn
+++ b/config/compiler/BUILD.gn
@@ -1379,6 +1379,8 @@ config("default_warnings") {
 
       "/wd4715",  # 'function' : not all control paths return a value'
                   # MSVC does not analyze switch (enum) for completeness.
+
+      "/wd4018",  # signed/unsigned mismatch in h265 codec.
     ]
 
     cflags_cc += [
@@ -1480,6 +1482,7 @@ config("default_warnings") {
       cflags += [
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
+        "-Wno-deprecated-declarations", # 'OSAtomicCompareAndSwap32Barrier' is deprecated: first deprecated in macOS 10.12
       ]
 
       if (is_win) {
@@ -1488,7 +1491,7 @@ config("default_warnings") {
         cflags += [ "-Wno-nonportable-include-path" ]
       }
 
-      if (current_toolchain == host_toolchain || !use_xcode_clang) {
+      if (current_toolchain == host_toolchain && !use_xcode_clang) {
         # Flags NaCl (Clang 3.7) and Xcode 9.2 (Clang clang-900.0.39.2) do not
         # recognize.
         cflags += [
@@ -1528,6 +1531,24 @@ config("default_warnings") {
         ]
       }
     }
+  } else if (!is_win) {
+    cflags += [
+      "-Wno-attributes",
+      "-Wno-address",
+      "-Wno-nonnull-compare",
+      "-Wno-return-type",
+      "-Wno-dangling-else",
+      "-Wno-sequence-point",
+      "-Wno-sign-compare",
+      "-Wno-unused-but-set-variable",
+      "-Wno-int-in-bool-context",
+      "-Wno-unused-function",
+      "-Wno-parentheses",
+    ]
+    cflags_cc += [
+      "-Wno-subobject-linkage",
+      "-Wno-register",
+    ]
   }
 }
 
@@ -1660,7 +1681,7 @@ config("no_chromium_code") {
       # suppressing them individually, we just blanket suppress them here.
       "-Wno-unused-variable",
     ]
-    if (!is_nacl && (current_toolchain == host_toolchain || !use_xcode_clang)) {
+    if (!is_nacl && (current_toolchain == host_toolchain && !use_xcode_clang)) {
       cflags += [
         # TODO(https://crbug.com/1031169): Clean up and enable.
         "-Wno-misleading-indentation",
diff --git a/config/gcc/BUILD.gn b/config/gcc/BUILD.gn
index 747245f37..6e35afbf8 100644
--- a/config/gcc/BUILD.gn
+++ b/config/gcc/BUILD.gn
@@ -91,7 +91,8 @@ if (is_component_build && !is_android) {
 # Settings for executables.
 config("executable_config") {
   configs = executable_and_shared_library_configs_
-  ldflags = [ "-pie" ]
+  # ldflags = [ "-pie" ]
+  ldflags = []
   if (is_android) {
     ldflags += [
       "-Bdynamic",
diff --git a/config/linux/gtk/gtk.gni b/config/linux/gtk/gtk.gni
index 0a3f35db9..b23571a3e 100644
--- a/config/linux/gtk/gtk.gni
+++ b/config/linux/gtk/gtk.gni
@@ -12,4 +12,4 @@ declare_args() {
   gtk_version = 3
 }
 
-assert(gtk_version >= 3 && gtk_version <= 4)
+assert(gtk_version >= 2 && gtk_version <= 4)
diff --git a/toolchain/mac/BUILD.gn b/toolchain/mac/BUILD.gn
index 08b17ff65..766188582 100644
--- a/toolchain/mac/BUILD.gn
+++ b/toolchain/mac/BUILD.gn
@@ -86,7 +86,7 @@ template("mac_toolchain") {
 
     # Supports building with the version of clang shipped with Xcode when
     # targeting iOS by not respecting clang_base_path.
-    if (toolchain_args.current_os == "ios" && use_xcode_clang) {
+    if (use_xcode_clang) {
       prefix = ""
     } else {
       prefix = rebase_path("$clang_base_path/bin/", root_build_dir)
diff --git a/toolchain/toolchain.gni b/toolchain/toolchain.gni
index 552ceb67e..71f2f6498 100644
--- a/toolchain/toolchain.gni
+++ b/toolchain/toolchain.gni
@@ -45,8 +45,8 @@ declare_args() {
 # Check target_os here instead of is_ios as this file is loaded for secondary
 # toolchain (host toolchain in particular) but the argument is the same for
 # all toolchains.
-assert(!use_xcode_clang || target_os == "ios",
-       "Using Xcode's clang is only supported in iOS builds")
+# assert(!use_xcode_clang || target_os == "ios",
+#        "Using Xcode's clang is only supported in iOS builds")
 
 # Extension for shared library files (including leading dot).
 if (is_mac || is_ios) {