gdb: fix gdbarch_tdep ODR violation

I would like to be able to use non-trivial types in gdbarch_tdep types.
This is not possible at the moment (in theory), because of the one
definition rule.

To allow it, rename all gdbarch_tdep types to <arch>_gdbarch_tdep, and
make them inherit from a gdbarch_tdep base class.  The inheritance is
necessary to be able to pass pointers to all these <arch>_gdbarch_tdep
objects to gdbarch_alloc, which takes a pointer to gdbarch_tdep.

These objects are never deleted through a base class pointer, so I
didn't include a virtual destructor.  In the future, if gdbarch objects
deletable, I could imagine that the gdbarch_tdep objects could become
owned by the gdbarch objects, and then it would become useful to have a
virtual destructor (so that the gdbarch object can delete the owned
gdbarch_tdep object).  But that's not necessary right now.

It turns out that RISC-V already has a gdbarch_tdep that is
non-default-constructible, so that provides a good motivation for this
change.

Most changes are fairly straightforward, mostly needing to add some
casts all over the place.  There is however the xtensa architecture,
doing its own little weird thing to define its gdbarch_tdep.  I did my
best to adapt it, but I can't test those changes.

Change-Id: Ic001903f91ddd106bd6ca09a79dabe8df2d69f3b

1 files changed, 17 insertions, 16 deletions

diff --git a/gdb/s390-tdep.h b/gdb/s390-tdep.h
index 8c9d75a..191977e 100644
--- a/gdb/s390-tdep.h
+++ b/gdb/s390-tdep.h
@@ -37,32 +37,33 @@ enum s390_vector_abi_kind
 
 /* The tdep structure.  */
 
-struct gdbarch_tdep
+struct s390_gdbarch_tdep : gdbarch_tdep
 {
   /* Target description.  */
-  const struct target_desc *tdesc;
+  const struct target_desc *tdesc = nullptr;
 
   /* ABI version.  */
-  enum s390_abi_kind abi;
+  enum s390_abi_kind abi {};
 
   /* Vector ABI.  */
-  enum s390_vector_abi_kind vector_abi;
+  enum s390_vector_abi_kind vector_abi {};
 
   /* Pseudo register numbers.  */
-  int gpr_full_regnum;
-  int pc_regnum;
-  int cc_regnum;
-  int v0_full_regnum;
-
-  bool have_upper;
-  bool have_linux_v1;
-  bool have_linux_v2;
-  bool have_tdb;
-  bool have_vx;
-  bool have_gs;
+  int gpr_full_regnum = 0;
+  int pc_regnum = 0;
+  int cc_regnum = 0;
+  int v0_full_regnum = 0;
+
+  bool have_upper = 0;
+  bool have_linux_v1 = 0;
+  bool have_linux_v2 = 0;
+  bool have_tdb = 0;
+  bool have_vx = 0;
+  bool have_gs = 0;
 
   /* Hook to record OS specific systemcall.  */
-  int (*s390_syscall_record) (struct regcache *regcache, LONGEST svc_number);
+  int (*s390_syscall_record) (struct regcache *regcache, LONGEST svc_number)
+    = nullptr;
 };
 
 /* Decoding S/390 instructions.  */