[Driver][Fuchsia] Pass --hash-style=gnu to the linker

[mcgrathr]

Summary

The .gnu_hash format is superior, and all versions of the Fuchsia
dynamic linker support it.

[mcgrathr]

Added test.

[phosek]

LGTM

lib/Driver/ToolChains/Fuchsia.cpp

void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (Args.hasArg(options::OPT_rdynamic))
     CmdArgs.push_back("-export-dynamic");
 
   if (Args.hasArg(options::OPT_s))
     CmdArgs.push_back("-s");
 
   if (Args.hasArg(options::OPT_r))
     CmdArgs.push_back("-r");
-  else
+  else {
     CmdArgs.push_back("--build-id");
+    CmdArgs.push_back("--hash-style=gnu");
+  }
 
   if (!Args.hasArg(options::OPT_static))
     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");

test/Driver/fuchsia.c

 // RUN: %clang %s -### -no-canonical-prefixes --target=x86_64-unknown-fuchsia \
 // RUN:     --sysroot=%S/platform -fuse-ld=ld 2>&1 | FileCheck %s
 // CHECK: {{.*}}clang{{.*}}" "-cc1"
 // CHECK: "-fuse-init-array"
 // CHECK: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK: "-internal-externc-isystem" "[[SYSROOT]]{{/|\\\\}}include"
 // CHECK: {{.*}}lld{{.*}}" "-flavor" "gnu"
 // CHECK: "-z" "rodynamic"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
+// CHECK: "--hash-style=gnu"
 // CHECK: "-dynamic-linker" "ld.so.1"
 // CHECK: Scrt1.o
 // CHECK-NOT: crti.o
 // CHECK-NOT: crtbegin.o
 // CHECK: "-L[[SYSROOT]]{{/|\\\\}}lib"
 // CHECK: "{{.*[/\\]}}libclang_rt.builtins-x86_64.a"
 // CHECK: "-lc"
 // CHECK-NOT: crtend.o