Move libc++ configs and flags out of //build/config/sanitizers

build/config/sanitizers/sanitizers.gni

Index: build/config/sanitizers/sanitizers.gni
diff --git a/build/config/sanitizers/sanitizers.gni b/build/config/sanitizers/sanitizers.gni
index 076206a07446eabb27fd4f76547e03e3d750844d..73ead4fe974e46920663c73562cfcf9944421cf6 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -126,7 +126,6 @@ if (current_toolchain != default_toolchain) {
   use_afl = false
   use_cfi_diag = false
   use_cfi_recover = false
-  use_custom_libcxx = false
   use_drfuzz = false
   use_libfuzzer = false
   use_prebuilt_instrumented_libraries = false
@@ -138,13 +137,6 @@ if (current_toolchain != default_toolchain) {
 # declare_args block. User overrides are only applied at the end of a
 # declare_args block.
 declare_args() {
-  # Use libc++ (buildtools/third_party/libc++ and
-  # buildtools/third_party/libc++abi) instead of stdlibc++ as standard library.
-  # This is intended to be used for instrumented builds.
-  use_custom_libcxx =
-      (is_asan && is_linux && !is_chromeos) || is_tsan || is_msan || is_ubsan ||
-      is_ubsan_security || (use_libfuzzer && !is_mac) || use_afl
-
   # Enable -fsanitize-coverage.
   use_sanitizer_coverage =
       use_libfuzzer || use_afl || sanitizer_coverage_flags != ""