Fix the gdb.dwarf2/dw2-dir-file-name.exp test on MIPS

Fix the gdb.dwarf2/dw2-dir-file-name.exp test on MIPS

This patch fixes the failures that occur with the
gdb.dwarf2/dw2-dir-file-name.exp test on 64-bit MIPS and compressed
MIPS ISAs (i.e. MIPS16 and microMIPS).

The failures on 64-bit occur because the generated DWARF address
information is always 32-bit, which causes the upper 32-bits of
addresses to be truncated and causes breakpoints to be set on the
wrong address if any of the upper 32-bits are non-zero.  I suspect
that other 64-bit architectures get away with it because they
place all their instructions at a VMA lower than 2^32 by default.
This patch causes 64-bit addresses to be generated if a 64-bit
target is detected.

The failures on MIPS16 and microMIPS occur because the breakpoint
address needs to have the LSB set to 1 (used to indicate that the
code is compressed). However, the function name is interpreted as
a data label, causing GDB to set breakpoints at even addresses.
This is fixed by explicitly adding a '.insn' directive (see
https://sourceware.org/binutils/docs/as/MIPS-insn.html) after the
label on MIPS only.

gdb/testsuite/

2014-10-18  Kwok Cheung Yeung  <kcy@codesourcery.com>

	* gdb.dwarf2/dw2-dir-file-name.exp (addr_len): New.
	(out_cu): Use addr_len for the size of addresses.
	(out_line): Likewise.  Size DW_LNE_set_address instruction
	according to addr_len.
	* gdb.dwarf2/dw2-dir-file-name.c (START_INSNS): New.
	(FUNC): Add START_INSNS to definition.