Fix dw2-ifort-parameter.exp fail with clang

Fix dw2-ifort-parameter.exp fail with clang

The patch <https://sourceware.org/ml/gdb-patches/2014-03/msg00202.html>
fixed dw2-ifort-parameter.exp on powerpc64 by adding some labels to
get the start and end address of function func.  This should also fix the
fail on thumb mode, however, this style is quite specific to gcc, and
other compiler, such as clang, may not guarantee the order of global
asms and functions.  The test fails with clang:

$ make check RUNTESTFLAGS='dw2-ifort-parameter.exp CC_FOR_TARGET=clang'
(gdb) p/x param^M
No symbol "param" in current context.^M
(gdb) FAIL: gdb.dwarf2/dw2-ifort-parameter.exp: p/x param

With this patch applied, dw2-ifort-parameter.exp still passes for gcc
on arm thumb mode and popwerpc64, and it also passes for clang on
x86_linux.

gdb/testsuite:

2014-11-14  Yao Qi  <yao@codesourcery.com>

	* gdb.dwarf2/dw2-ifort-parameter.c: Remove inline asm.
	(func): Add label func_label.
	* gdb.dwarf2/dw2-ifort-parameter.exp (Dwarf::assemble):
	Replace low_pc and high_pc with MACRO_AT_range.
	Replace name, low_pc and high_pc with MACRO_AT_func.