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, 11 insertions, 11 deletions

diff --git a/gdb/m68k-tdep.h b/gdb/m68k-tdep.h
index 16384d1..c88e7f2 100644
--- a/gdb/m68k-tdep.h
+++ b/gdb/m68k-tdep.h
@@ -67,38 +67,38 @@ enum m68k_flavour
 
 /* Target-dependent structure in gdbarch.  */
 
-struct gdbarch_tdep
+struct m68k_gdbarch_tdep : gdbarch_tdep
 {
   /* Offset to PC value in the jump buffer.  If this is negative,
      longjmp support will be disabled.  */
-  int jb_pc;
+  int jb_pc = 0;
   /* The size of each entry in the jump buffer.  */
-  size_t jb_elt_size;
+  size_t jb_elt_size = 0;
 
   /* Register in which the address to store a structure value is
      passed to a function.  */
-  int struct_value_regnum;
+  int struct_value_regnum = 0;
 
   /* Register in which a pointer value is returned.  In the SVR4 ABI,
      this is %a0, but in GCC's "embedded" ABI, this is %d0.  */
-  int pointer_result_regnum;
+  int pointer_result_regnum = 0;
 
   /* Convention for returning structures.  */
-  enum struct_return struct_return;
+  enum struct_return struct_return {};
 
   /* Convention for returning floats.  zero in int regs, non-zero in float.  */
-  int float_return;
+  int float_return = 0;
 
   /* The particular flavour of m68k.  */
-  enum m68k_flavour flavour;
+  enum m68k_flavour flavour {};
 
   /* Flag set if the floating point registers are present, or assumed
      to be present.  */
-  int fpregs_present;
+  int fpregs_present = 0;
 
    /* ISA-specific data types.  */
-  struct type *m68k_ps_type;
-  struct type *m68881_ext_type;
+  struct type *m68k_ps_type = nullptr;
+  struct type *m68881_ext_type = nullptr;
 };
 
 /* Initialize a SVR4 architecture variant.  */