Correctly handle non-C-style arrays in c_get_string

Correctly handle non-C-style arrays in c_get_string

A user here noticed that the Python Value.string method did not work
for Ada arrays.  I tracked this down to an oddity in value_as_address
-- namely, it calls coerce_array, but that function will not force
array coercion when the language has c_style_arrays=false, as Ada
does.

This patch fixes the problem by changing c_get_string so that arrays
take the "in GDB's memory" branch.  The actual patch is somewhat more
complicated than you might think, because the caller can request more
array elements than the type allows.  This is normal when the type is
using the C struct hack.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-05-08  Tom Tromey  <tromey@adacore.com>

	* c-lang.c (c_get_string): Handle non-C-style arrays.

gdb/testsuite/ChangeLog
2019-05-08  Tom Tromey  <tromey@adacore.com>

	* gdb.python/py-value.exp (test_value_in_inferior): Add Ada test.