Add dwarf support

The new gcc12 release does not support stabs any more.
This was a good reason to add support for dwarf.

The stabs code still works and is used if configure option --dwarf
is not used.

Tested on x86_64, i386, arm, arm64, riscv64 with dwarf-5.
Some debuggers may not support dwarf-5. Try using older dwarf versions
i that case.
The tccmacho.c code probably need some support for dwarf.

arm-gen.c, arm64-gen.c, i386-gen.c, riscv64-gen.c, x86_64-gen.
- fix get_sym_ref symbol size

arm-link.c, arm64-link.c, i386-link.c, riscv64-link.c, x86_64-link.c
- add R_DATA_32U

libtcc.c:
- parse -gdwarf option

tcc.c:
- add dwarf option

tcc.h:
- add dwarf option and sections

tccelf.c:
- init dwarf sections
- avoid adding sh_addr for dwarf sections
- remove dwarf relocs for output dll
- add dwarf sections for tccrun

tccgen.c:
- add dwarf defines + global data
- add dwarf_* functions
- mix dwarf code with stabs code
- a trick is used to emit function name in .debug_line section so
  only this section has to be parsed instead of .debug_info and
  .debug_abbrev.
- fix init debug_modes

tccrun.c:
- add dwarf sections in rt_context
- init them in tcc_run
- add new dwarf code rt_printline_dwarf to find file/function

dwarf.h:
- New file

tcc-doc.texi:
- document dwarf

configure:
- add dwarf option

lib/Makefile
- change -gstabs into -gdwarf

lib/bt-exe.c, tests/tests2/Makefile, tests/tests2/126_bound_global:
- Add __bound_init call
- Add new testcase to test it

lib/bt-exe.c

@@ -18,6 +18,10 @@ void __bt_init(rt_context *p, int num_callers)
     __attribute__((weak)) void __bound_init(void*, int);
     struct rt_context *rc = &g_rtctxt;
     //fprintf(stderr, "__bt_init %d %p %p\n", num_callers, p->stab_sym, p->bounds_start), fflush(stderr);
+    /* call __bound_init here due to redirection of sigaction */
+    /* needed to add global symbols */
+    if (__bound_init && p->bounds_start)
+	__bound_init(p->bounds_start, -1);
     if (num_callers) {
         memcpy(rc, p, offsetof(rt_context, next));
         rc->num_callers = num_callers - 1;