[ppc64] Fix for function descriptors

[ppc64] Fix for function descriptors

Marin Cermak has found various testcases (or one of them) of GDB FAIL on
ppc64.

https://sourceware.org/bugzilla/show_bug.cgi?id=20328

.o contained only the function descriptor address.

The DWARF as produced by Tcl Dwarf::assemble:
 <1><27>: Abbrev Number: 4 (DW_TAG_subprogram)
    <28>   DW_AT_name        : main
    <2d>   DW_AT_external    : 1
    <2e>   DW_AT_low_pc      : 0x1001ff98
    <36>   DW_AT_high_pc     : 0x1002ff98
 <2><3e>: Abbrev Number: 5 (DW_TAG_lexical_block)

Runtime info:
$2 = {<text variable, no debug info>} 0x10000674 <.main>
$3 = {void ()} 0x1001ff98 <main>

On Tue, 12 Jul 2016 15:22:49 +0200, Ulrich Weigand wrote:
Well, most of the gdb.dwarf2 test cases simply use explicitly placed labels
for the DW_AT_low_pc / DW_AT_high_pc attributes.

See e.g. dw2-unresolved-main.c:

asm (".globl cu_text_start");
asm ("cu_text_start:");

On Wed, 13 Jul 2016 10:54:00 +0200, Jan Kratochvil wrote:
Now I see I should not do that because:

lib/dwarf.exp:
proc function_range { func src } {

So I am providing this patch.

gdb/testsuite/ChangeLog
2016-07-13  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.dwarf2/atomic-type.exp: Use function_range for low_pc and high_pc.
	* gdb.dwarf2/atomic.c (f): Rename f_end_lbl to f_label.
	* gdb.dwarf2/dw2-bad-mips-linkage-name.c (f): Rename f_end_lbl to
	f_label.
	(g): Rename g_end_lbl to g_label.
	* gdb.dwarf2/dw2-bad-mips-linkage-name.exp: Use function_range for
	low_pc and high_pc.
	* gdb.dwarf2/dw2-lexical-block-bare.exp: Likewise.