[Driver] Make --execute-only the default for aarch64-fuchsia

[abrachet]

Summary

Clang already generates code that doesn't use writeable data in executable
sections so the linker flag is all that is necessary.

-Wl,--no-execute-only can be used to turn this default off.

[mcgrathr]

clang/lib/Driver/ToolChains/Fuchsia.cpp

95

This is a little confusing to read when it's after the other lines.
I'd put it first in the block with a blank line after it.

[abrachet]

clang/lib/Driver/ToolChains/Fuchsia.cpp

95

Fixed in commit

clang/lib/Driver/ToolChains/Fuchsia.cpp

void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (Args.hasArg(options::OPT_r)) {
     CmdArgs.push_back("-r");
   } else {
     CmdArgs.push_back("--build-id");
     CmdArgs.push_back("--hash-style=gnu");
   }
 
   if (ToolChain.getArch() == llvm::Triple::aarch64) {
+    CmdArgs.push_back("--execute-only");
+
     std::string CPU = getCPUName(D, Args, Triple);
     if (CPU.empty() || CPU == "generic" || CPU == "cortex-a53")
       CmdArgs.push_back("--fix-cortex-a53-843419");
   }
 
   CmdArgs.push_back("--eh-frame-hdr");
 
   if (Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-Bstatic");
   else if (Args.hasArg(options::OPT_shared))
     CmdArgs.push_back("-shared");
 

clang/test/Driver/fuchsia.c

 // CHECK: "-stack-protector" "2"
 // CHECK-AARCH64: "-target-feature" "+outline-atomics"
 // CHECK-NOT: "-fcommon"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "max-page-size=4096" "-z" "now" "-z" "rodynamic" "-z" "separate-loadable-segments" "-z" "rel" "--pack-dyn-relocs=relr"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
 // CHECK: "--hash-style=gnu"
-// CHECK-AARCH64: "--fix-cortex-a53-843419"
+// CHECK-AARCH64: "--execute-only" "--fix-cortex-a53-843419"
 // CHECK: "-dynamic-linker" "ld.so.1"
 // CHECK-RISCV64: "-X"
 // CHECK: Scrt1.o
 // CHECK-NOT: crti.o
 // CHECK-NOT: crtbegin.o
 // CHECK: "-L[[SYSROOT]]{{/|\\\\}}lib"
 // CHECK-X86_64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"