[binutils-gdb] Tweak the std::hash<> specialization for aarch64_features.

[binutils-gdb] Tweak the std::hash<> specialization for aarch64_features.

[John Baldwin]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=e8123c847f61c7458200b349615c47e9df17a0ed

commit e8123c847f61c7458200b349615c47e9df17a0ed
Author: John Baldwin <jhb@FreeBSD.org>
Date:   Mon May 23 11:02:55 2022 -0700

    Tweak the std::hash<> specialization for aarch64_features.
    
    Move the specialization into an explicit std namespace to workaround a
    bug in older compilers.  GCC 6.4.1 at least fails to compile the previous
    version with the following error:
    
    gdb/arch/aarch64.h:48:13: error: specialization of 'template<class _Tp> struct std::hash' in different namespace [-fpermissive]
    
      struct std::hash<aarch64_features>

Diff:
---
 gdb/arch/aarch64.h | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/gdb/arch/aarch64.h b/gdb/arch/aarch64.h
index 72ec4193eba..8e3fd36726a 100644
--- a/gdb/arch/aarch64.h
+++ b/gdb/arch/aarch64.h
@@ -44,20 +44,23 @@ inline bool operator==(const aarch64_features &lhs, const aarch64_features &rhs)
     && lhs.tls == rhs.tls;
 }
 
-template<>
-struct std::hash<aarch64_features>
+namespace std
 {
-  std::size_t operator()(const aarch64_features &features) const noexcept
+  template<>
+  struct hash<aarch64_features>
   {
-    std::size_t h;
-
-    h = features.vq;
-    h = h << 1 | features.pauth;
-    h = h << 1 | features.mte;
-    h = h << 1 | features.tls;
-    return h;
-  }
-};
+    std::size_t operator()(const aarch64_features &features) const noexcept
+    {
+      std::size_t h;
+
+      h = features.vq;
+      h = h << 1 | features.pauth;
+      h = h << 1 | features.mte;
+      h = h << 1 | features.tls;
+      return h;
+    }
+  };
+}
 
 /* Create the aarch64 target description.  */