gas: Use udata for DW_AT_high_pc when emitting DWARF4 (Was: Broken GAS DWARF tests)

[Fangrui Song]

On 2020-08-04, Alan Modra via Binutils wrote:
>On Mon, Aug 03, 2020 at 10:11:27PM +0200, Mark Wielaard wrote:
>>        * dwarf2dbg.c (out_debug_abbrev): When DWARF2_VERSION >= 4, use
>>        DW_FORM_udata for DW_AT_high_pc.
>>        (out_debug_info): Use emit_leb128_expr for DW_AT_high_pc, when
>>        DWARF2_VERSION >= 4.
>>        * read.c (emit_leb128_exp): No longer static.
>>        * read.h (emit_leb128_exp): Define.
>
>OK, looks good.  Note that there have been problems in the past
>resolving leb128 expressions (eg. see 38cf168be581), so please keep an
>eye out for regressions.
>
>-- 
>Alan Modra
>Australia Development Lab, IBM

Using DWARF v3 attribute class 'address' for DW_AT_high_pc can save a
relocation on RISC-V in -mrelax mode