fix some gdb.dwarf2 tests for parallel safety

fix some gdb.dwarf2 tests for parallel safety

This fixes a few gdb.dwarf2 tests to be more parallel-safe.  This
mostly amounts to changing them to write their files into the
directory designated by standard_output_file.

Built and regtested on x86-64 Fedora 18.

	* gdb.dwarf2/clztest.exp: Use standard_testfile.
	* gdb.dwarf2/dw2-minsym-in-cu.exp: Use standard_testfile.
	* gdb.dwarf2/fission-base.S: Remove directory from
	DW_AT_GNU_dwo_name.
	* gdb.dwarf2/fission-base.exp: Use build_executable.  Set
	debug-file-directory.
	* gdb.dwarf2/fission-reread.S: Remove directory from
	DW_AT_GNU_dwo_name.
	* gdb.dwarf2/fission-reread.exp: Use build_executable.  Set
	debug-file-directory.