The testcase was generating DW_AT_high_pc and DW_AT_low_pc entries

The testcase was generating DW_AT_high_pc and DW_AT_low_pc entries
with type DW_FORM_string, which is wrong.

GDB was using that information to load data as strings, and then
proceeded to use the string pointers as addresses.

Even then, the test was passing just fine, because we were lucky
enough to have the low_pc string pointer smaller than the high_pc
string pointer.

Two issues are fixed.  The first one is the DW_FORM_string type. The
second one is adjusting the addresses so that they are non-zero,
since GDB doesn't like seeing 0 in these fields due to a check
contained in dwarf2_get_pc_bounds:

  if (low == 0 && !dwarf2_per_objfile->has_section_at_zero)
    return 0;

With both fixes, the testcase passes deterministically.

2014-06-19  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.cp/nsalias.exp: Set type of low_pc and high_pc entries
	to DW_FORM_addr and use non-zero addresses.