ld/testsuite: handle Windows drive letter in a noinit test

The regexp in "noinit sections (ld -r)" is skipping the file path before
the first ":". However, on Windows, a path can start with "C:". Adjust
the regexp to allow such cases.

ld/ChangeLog:

	* testsuite/ld-elf/noinit-sections-2.l: Allow Windows paths
	(starting with C:).