Relax gdb.compile/compile.exp to match the address printed for frame

Relax gdb.compile/compile.exp to match the address printed for frame

One test in gdb.compile/compile.exp passes on one fedora builder,

 bt
 #0  0x00007ffff7ff43f6 in _gdb_expr (__regs=0x7ffff7ff2000) at gdb
 command line:1^M
 #1  <function called from gdb>^M
 #2  main () at /home/gdb-buildbot/fedora-x86-64-1/fedora-x86-64/build/gdb/testsuite/../../../binutils-gdb/gdb/testsuite/gdb.compile/compile.c:106^M
 (gdb) PASS: gdb.compile/compile.exp: bt

but fails on my machine with gcc trunk,

 bt^M
 #0  _gdb_expr (__regs=0x7ffff7ff3000) at gdb command line:1^M
 #1  <function called from gdb>^M
 #2  main () at gdb/testsuite/gdb.compile/compile.c:106^M
 (gdb) FAIL: gdb.compile/compile.exp: bt

The test should be tweaked to match both cases (pc in the start of line
vs pc in the middle of line).  Note that I am not clear that why libcc1
emits debug info this way so that the address is in the middle of line.

gdb/testsuite:

2018-01-17  Yao Qi  <yao.qi@linaro.org>

	* gdb.compile/compile.exp: Match the address printed for
	frame in the output of command "bt".