[build] Cleanup TODO for TLSDESC compiler flags

After llvm/llvm-project#124990, LLVM sets
TLSDESC as the default for Fuchsia targets. This patch moves the config
setting into clang_defaults.

Fixed: 322984857
Change-Id: Idca5a2c13e7f2128a5c28b337689db4ed4caf1ba
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1265705
Fuchsia-Auto-Submit: Paul Kirth <[email protected]>
Reviewed-by: Roland McGrath <[email protected]>
Commit-Queue: Auto-Submit <auto-submit-builder@fuchsia-internal-service-accts.iam.gserviceaccount.com>

Author: ilovepi

build/config/BUILD.gn

@@ -125,12 +125,9 @@ config("compiler") {
     ":stack-size-section",
   ]
 
-  # TODO(https://fxbug.dev/322984857): Only add this config for is_gcc configs
-  # after we roll a toolchain with default TLSDESC for Fuchsia targets, at
-  # which point it can be moved into clang_defaults.
-  configs += [ ":default-tls-dialect" ]
-
-  if (!is_gcc) {
+  if (is_gcc) {
+    configs += [ ":default-tls-dialect" ]
+  } else {
     configs += [
       ":clang_defaults",
       ":embed_bitcode",
@@ -194,7 +191,6 @@ config("clang_defaults") {
     cflags_cc = [ "-stdlib=libc++" ]
     ldflags = [
       "-stdlib=libc++",
-
       "--start-no-unused-arguments",
       "-unwindlib=libunwind",
       "-rtlib=compiler-rt",
@@ -1584,15 +1580,15 @@ tlsdesc = {
     # On riscv64 TLSDESC is opt-in or opt-out via -mtls-dialect=... under Clang, but is not currently supported in GCC.
     can_enable = !is_gcc
     can_disable = !is_gcc
-    compiler_default = false
+    compiler_default = !is_gcc
   } else if (current_cpu == "x64") {
     enable_dialect = "gnu2"
     disable_dialect = "gnu"
     have_tlsdesc = 1
 
     can_enable = true
     can_disable = true
-    compiler_default = false
+    compiler_default = !is_gcc
   } else if (current_cpu == "arm") {
     enable_dialect = "gnu2"
     disable_dialect = "gnu"