Fix -Wpointer-sign around strings/encoding conversions.

Fix -Wpointer-sign around strings/encoding conversions.

Trimmed for brevity:

$ make WERROR_CFLAGS="-Wpointer-sign -Werror" c-lang.o expprint.o utils.o valprint.o varobj.o -k 2>&1 1>/dev/null
../../src/gdb/c-lang.c: In function ‘parse_one_string’:
../../src/gdb/c-lang.c:540:8: error: pointer targets in passing argument 3 of ‘convert_between_encodings’ differ in signedness [-Werror=pointer-sign]
In file included from ../../src/gdb/c-lang.c:30:0:
../../src/gdb/charset.h:64:6: note: expected ‘const gdb_byte *’ but argument is of type ‘char *’

../../src/gdb/expprint.c: In function ‘print_subexp_standard’:
../../src/gdb/expprint.c:205:2: error: pointer targets in passing argument 3 of ‘current_language->la_printstr’ differ in signedness [-Werror=pointer-sign]
../../src/gdb/expprint.c:205:2: note: expected ‘const gdb_byte *’ but argument is of type ‘char *’

cc1: all warnings being treated as errors
make: *** [expprint.o] Error 1
../../src/gdb/utils.c: In function ‘host_char_to_target’:
../../src/gdb/utils.c:1474:9: error: pointer targets in passing argument 3 of ‘convert_between_encodings’ differ in signedness [-Werror=pointer-sign]

../../src/gdb/varobj.c: In function ‘value_get_print_value’:
../../src/gdb/varobj.c:2934:8: error: pointer targets in return differ in signedness [-Werror=pointer-sign]
../../src/gdb/varobj.c:2968:12: error: pointer targets in assignment differ in signedness [-Werror=pointer-sign]
../../src/gdb/varobj.c:2971:3: error: pointer targets in return differ in signedness [-Werror=pointer-sign]
cc1: all warnings being treated as errors
make: *** [varobj.o] Error 1

As with the previous patch, the encoding conversion code works with
gdb_byte arrays as the generic buffers that hold strings of any
encoding/width.  This patch adds casts where appropriate.

gdb/
2013-03-07  Pedro Alves  <palves@redhat.com>

	* c-lang.c (parse_one_string): Cast argument to gdb_byte *.
	* expprint.c (print_subexp_standard): Likewise.
	* utils.c (host_char_to_target): Likewise.
	* valprint.c (generic_emit_char, generic_printstr): Likewise.
	* varobj.c (value_get_print_value): Change type of local to char*.
	Cast it gdb_byte * in call to language printer.