Powerpc fix for gdb.base/unwind-on-each-insn.exp

Powerpc fix for gdb.base/unwind-on-each-insn.exp

The test disassembles function foo and searches for the line
"End of assembler dump" to determing the last address in the function.  The
assumption is the last instruction will be given right before the line
"End of assembler dump".  This assumption fails on PowerPC.

The PowerPC disassembly of the function foo looks like:
 Dump of assembler code for function foo:
#  => 0x00000000100006dc <+0>:     std     r31,-8(r1)
#     0x00000000100006e0 <+4>:     stdu    r1,-48(r1)
#     0x00000000100006e4 <+8>:     mr      r31,r1
#     0x00000000100006e8 <+12>:    nop
#     0x00000000100006ec <+16>:    addi    r1,r31,48
#     0x00000000100006f0 <+20>:    ld      r31,-8(r1)
#     0x00000000100006f4 <+24>:    blr
#     0x00000000100006f8 <+28>:    .long 0x0
#     0x00000000100006fc <+32>:    .long 0x0
#     0x0000000010000700 <+36>:    .long 0x1000180
#     End of assembler dump.

The blr instruction is the last instruction in function foo.  The lines
with .long following the blr instruction need to be ignored.

This patch adds a new condition to the gdb_test_multiple "disassemble foo"
test to ignore the lines with the .long.

The patch has been tested on PowerPC and Intel X86-64.