DWARF: space-optimize loc. descr. for integer literals on 32-bit targets

DWARF: space-optimize loc. descr. for integer literals on 32-bit targets

This enhances location description generation so that the generated
opcodes for integer literals are as space-efficient when HOST_WIDE_INT
is 64-bits large than when it's 32-bits large. In particular, this
reduces the size of the opcodes generated to produce big unsigned
literals using small literal integers instead.

gcc/

	* dwarf2out.c (int_loc_descriptor): Generate opcodes for another
	equivalent 32-bit constant (modulo 2**32) when that yields
	smaller instructions.
	(size_of_int_loc_descriptor): Update accordingly.

gcc/testsuite/

	* gnat.dg/debug8.adb: New testcase.

From-SVN: r241024