gdb: Better support for dynamic properties with negative values

gdb: Better support for dynamic properties with negative values

When the type of a property is smaller than the CORE_ADDR in which the
property value has been placed, and if the property is signed, then
sign extend the property value from its actual type up to the size of
CORE_ADDR.

gdb/ChangeLog:

	* dwarf2loc.c (dwarf2_evaluate_property): Sign extend property
	value if its desired type is smaller than a CORE_ADDR and signed.

gdb/testsuite/ChangeLog:

	* gdb.fortran/vla-ptype.exp: Print array with negative bounds.
	* gdb.fortran/vla-sizeof.exp: Print the size of an array with
	negative bounds.
	* gdb.fortran/vla-value.exp: Print elements of an array with
	negative bounds.
	* gdb.fortran/vla.f90: Setup an array with negative bounds for
	testing.