diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 3b3cdd898..ed4baae3f 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -253,8 +253,6 @@ config("compiler") {
 
   configs += [
     # See the definitions below.
-    ":clang_revision",
-    ":compiler_cpu_abi",
     ":compiler_codegen",
     ":compiler_deterministic",
   ]
@@ -485,17 +483,6 @@ config("compiler") {
     ldflags += [ "-Wl,-z,keep-text-section-prefix" ]
   }
 
-  if (is_clang && !is_nacl && !use_xcode_clang) {
-    cflags += [ "-fcrash-diagnostics-dir=" + clang_diagnostic_dir ]
-
-    cflags += [
-      # TODO(hans): Remove this once Clang generates better optimized debug info
-      # by default. https://crbug.com/765793
-      "-mllvm",
-      "-instcombine-lower-dbg-declare=0",
-    ]
-  }
-
   # C11/C++11 compiler flags setup.
   # ---------------------------
   if (is_linux || is_android || (is_nacl && is_clang) || current_os == "aix") {
@@ -1061,14 +1048,6 @@ config("compiler_codegen") {
     ldflags += [ "-Wl,-mllvm,-enable-machine-outliner=never" ]
   }
 
-  if (is_clang && !is_nacl && !use_xcode_clang && !is_chromeos_device) {
-    cflags += [
-      # TODO(thakis): Remove after next clang roll, see reviews.llvm.org/D82998
-      "-mllvm",
-      "-basic-aa-recphi=0",
-    ]
-  }
-
   # TODO(thakis): Remove `if (!is_win)` after next clang roll.
   if (!is_win) {
     asmflags = cflags
@@ -1561,7 +1540,7 @@ config("chromium_code") {
       defines = [ "_HAS_NODISCARD" ]
     }
   } else {
-    cflags = [ "-Wall" ]
+    cflags = [ ]
     if (treat_warnings_as_errors) {
       cflags += [ "-Werror" ]
 
@@ -1570,10 +1549,6 @@ config("chromium_code") {
       # well.
       ldflags = [ "-Werror" ]
     }
-    if (is_clang) {
-      # Enable extra warnings for chromium_code when we control the compiler.
-      cflags += [ "-Wextra" ]
-    }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
@@ -1582,15 +1557,6 @@ config("chromium_code") {
       "__STDC_FORMAT_MACROS",
     ]
 
-    if (!is_debug && !using_sanitizer && current_cpu != "s390x" &&
-        current_cpu != "s390" && current_cpu != "ppc64" &&
-        current_cpu != "mips" && current_cpu != "mips64") {
-      # Non-chromium code is not guaranteed to compile cleanly with
-      # _FORTIFY_SOURCE. Also, fortified build may fail when optimizations are
-      # disabled, so only do that for Release build.
-      defines += [ "_FORTIFY_SOURCE=2" ]
-    }
-
     if (is_mac) {
       cflags_objc = [ "-Wobjc-missing-property-synthesis" ]
       cflags_objcc = [ "-Wobjc-missing-property-synthesis" ]
@@ -1988,7 +1954,8 @@ config("default_stack_frames") {
 }
 
 # Default "optimization on" config.
-config("optimize") {
+config("optimize") { }
+config("xoptimize") {
   if (is_win) {
     if (chrome_pgo_phase != 2) {
       # Favor size over speed, /O1 must be before the common flags.
@@ -2023,7 +1990,8 @@ config("optimize") {
 }
 
 # Turn off optimizations.
-config("no_optimize") {
+config("no_optimize") { }
+config("xno_optimize") {
   if (is_win) {
     cflags = [
       "/Od",  # Disable optimization.
@@ -2063,7 +2031,8 @@ config("no_optimize") {
 # Turns up the optimization level. On Windows, this implies whole program
 # optimization and link-time code generation which is very expensive and should
 # be used sparingly.
-config("optimize_max") {
+config("optimize_max") { }
+config("xoptimize_max") {
   if (is_nacl && is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # Various components do:
@@ -2095,7 +2064,8 @@ config("optimize_max") {
 #
 # TODO(crbug.com/621335) - rework how all of these configs are related
 # so that we don't need this disclaimer.
-config("optimize_speed") {
+config("optimize_speed") { }
+config("xoptimize_speed") {
   if (is_nacl && is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # Various components do:
@@ -2120,7 +2090,8 @@ config("optimize_speed") {
   }
 }
 
-config("optimize_fuzzing") {
+config("optimize_fuzzing") { }
+config("xoptimize_fuzzing") {
   cflags = [ "-O1" ] + common_optimize_on_cflags
   ldflags = common_optimize_on_ldflags
   visibility = [ ":default_optimization" ]
@@ -2237,7 +2208,8 @@ config("win_pdbaltpath") {
 }
 
 # Full symbols.
-config("symbols") {
+config("symbols") { }
+config("xsymbols") {
   if (is_win) {
     if (is_clang) {
       cflags = [ "/Z7" ]  # Debug information in the .obj files.
@@ -2344,7 +2316,8 @@ config("symbols") {
 # Minimal symbols.
 # This config guarantees to hold symbol for stack trace which are shown to user
 # when crash happens in unittests running on buildbot.
-config("minimal_symbols") {
+config("minimal_symbols") { }
+config("xminimal_symbols") {
   if (is_win) {
     # Functions, files, and line tables only.
     cflags = []
@@ -2401,7 +2374,8 @@ config("minimal_symbols") {
 # This configuration contains function names only. That is, the compiler is
 # told to not generate debug information and the linker then just puts function
 # names in the final debug information.
-config("no_symbols") {
+config("no_symbols") { }
+config("xno_symbols") {
   if (is_win) {
     ldflags = [ "/DEBUG" ]