[llvm] Enable TLSDESC by default on Fuchsia targets

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

@@ -1117,9 +1117,10 @@ 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 {