[llvm] Enable TLSDESC by default on Fuchsia targets (llvm#124990)

Fuchsia uses TLSDESC by default for all target architectures. We also
make the comment and check for hasDefaultTLSDESC more accurately reflect
its usage.

Author: ilovepi

clang/test/Driver/tls-dialect.c

@@ -10,6 +10,11 @@
 /// TLSDESC is not on by default in Linux, even on RISC-V, and is covered above
 // RUN: %clang -### --target=riscv64-android %s 2>&1 | FileCheck --check-prefix=DESC %s
 
+/// Fuchsia supports TLSDESC by default for all architectures.
+// RUN: %clang -### --target=riscv64-unknown-fuchsia %s 2>&1 | FileCheck --check-prefix=DESC %s
+// RUN: %clang -### --target=aarch64-unknown-fuchsia %s 2>&1 | FileCheck --check-prefix=DESC %s
+// RUN: %clang -### --target=x86_64-unknown-fuchsia %s 2>&1 | FileCheck --check-prefix=DESC %s
+
 /// LTO
 // RUN: %clang -### --target=loongarch64-linux -flto -mtls-dialect=desc %s 2>&1 | FileCheck --check-prefix=LTO-DESC %s
 // RUN: %clang -### --target=loongarch64-linux -flto %s 2>&1 | FileCheck --check-prefix=LTO-NODESC %s

llvm/include/llvm/TargetParser/Triple.h

@@ -1123,9 +1123,10 @@ class Triple {
            isWindowsCygwinEnvironment() || isOHOSFamily();
   }
 
-  /// True if the target supports both general-dynamic and TLSDESC, and TLSDESC
-  /// is enabled by default.
-  bool hasDefaultTLSDESC() const { return isAndroid() && isRISCV64(); }
+  /// True if the target uses TLSDESC by default.
+  bool hasDefaultTLSDESC() const {
+    return isAArch64() || (isAndroid() && isRISCV64()) || isOSFuchsia();
+  }
 
   /// Tests whether the target uses -data-sections as default.
   bool hasDefaultDataSections() const {