Allow a second -T<section>=<addr> to override a previous version on the same linker command line.

	PR ld/20302
	* lexsup.c (set_segment_start): If resetting the start address of
	a section, remember to generate a new script element as well.
	* testsuite/ld-scripts/pr20302.d: New test.
	* testsuite/ld-scripts/scripts.exp: Run the new test.