Remove restriction on skipping some linker tests because their default image base...

Remove restriction on skipping some linker tests because their default image base is too high.

	PR 25829
	* testsuite/ld-scripts/default-script.exp: Add --image-base=0 to
	LDFLAGS for targets *-*-mingw64 x86_64-*-cygwin.
	* testsuite/ld-scripts/default-script1.d: No longer have to skip
	test for those targets.
	* testsuite/ld-scripts/default-script2.d: Likewise.
	* testsuite/ld-scripts/default-script3.d: Likewise.
	* testsuite/ld-scripts/default-script4.d: Likewise.