[pushed] Fix GDB build with GCC 4.8.2

[Tom Tromey <tromey@adacore.com>]

PR build/27579 points out that the expression rewrite series
introduced a build failure with GCC 4.8.2.  The bug is that there's no
std::hash specialization for enum exp_opcode.  This patch fixes the
problem by using gdb::hash_enum.

2021-03-15  Tom Tromey  <tromey@adacore.com>

	PR build/27579:
	* rust-exp.y (maker_map): Use gdb::hash_enum.
	* stap-probe.c (stap_maker_map): Use gdb::hash_enum.
---
 gdb/ChangeLog    | 6 ++++++
 gdb/rust-exp.y   | 4 +++-
 gdb/stap-probe.c | 4 +++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/gdb/rust-exp.y b/gdb/rust-exp.y
index 9a5bdd7a836..04003409887 100644
--- a/gdb/rust-exp.y
+++ b/gdb/rust-exp.y
@@ -43,6 +43,7 @@
 #include "gdbarch.h"
 #include "rust-exp.h"
 #include <unordered_map>
+#include "gdbsupport/hash_enum.h"
 
 #define GDB_YY_REMAP_PREFIX rust
 #include "yy-remap.h"
@@ -2202,7 +2203,8 @@ typedef expr::operation_up binop_maker_ftype (expr::operation_up &&,
 /* Map from an expression opcode to a function that will create an
    instance of the appropriate operation subclass.  Only binary
    operations are handled this way.  */
-static std::unordered_map<exp_opcode, binop_maker_ftype *> maker_map;
+static std::unordered_map<exp_opcode, binop_maker_ftype *,
+			  gdb::hash_enum<exp_opcode>> maker_map;
 
 /* Lower a rust_op to a gdb expression.  STATE is the parser state.
    OPERATION is the operation to lower.  TOP is a pointer to the
diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c
index 5995c2824dc..7f6d98a8ef2 100644
--- a/gdb/stap-probe.c
+++ b/gdb/stap-probe.c
@@ -38,6 +38,7 @@
 #include "elf-bfd.h"
 #include "expop.h"
 #include <unordered_map>
+#include "gdbsupport/hash_enum.h"
 
 #include <ctype.h>
 
@@ -436,7 +437,8 @@ typedef expr::operation_up binop_maker_ftype (expr::operation_up &&,
 					      expr::operation_up &&);
 /* Map from an expression opcode to a function that can create a
    binary operation of that type.  */
-static std::unordered_map<exp_opcode, binop_maker_ftype *> stap_maker_map;
+static std::unordered_map<exp_opcode, binop_maker_ftype *,
+			  gdb::hash_enum<exp_opcode>> stap_maker_map;
 
 /* Helper function to create a binary operation.  */
 static expr::operation_up
-- 
2.26.2