Use safe-ctype.h (ISSPACE etc.) in symbol parsing & comparison

Use safe-ctype.h (ISSPACE etc.) in symbol parsing & comparison

This patch avoids depending on the current locale when parsing &
comparing symbol names, by using libiberty's safe-ctype.h uppercase
TOLOWER, ISXDIGIT, etc. macros instead of the standard ctype.h
tolower, isxdigit, etc. macros/functions.

This commit:

 commit b1b60145aedb8adcb0b9dcf43a5ae735c2f03b51
 Author:     Pedro Alves <palves@redhat.com>
 AuthorDate: Tue May 22 17:35:38 2018 +0100

    Support UTF-8 identifiers in C/C++ expressions (PR gdb/22973)

did something similar, except in the expression parser.

This can improve GDB's symbol loading performance significantly.
Currently strcmp_iw_ordered can show up high on profiles (called from
sort_pst_symbols -> std::sort) because of the isspace and tolower
functions.  Hannes mentions seeing it as high as in ~24% of the
profiling samples on Windows
(https://sourceware.org/pipermail/gdb-patches/2020-May/168858.html).

I tested GDB's performance (built with "-g -O2") loading a "-g -O0"
build of gdb.

I ran GDB 10 times like:

	  /bin/time -f %e \
		    ./gdb/gdb --data-directory ./gdb/data-directory -nx \
		    -batch /tmp/gdb-g-O0

Then I computed the mean time.

The baseline mean time was

 gdb    2.515

This patch brings the number down to

 gdb    2.096

Which is an around 16% improvement.

gdb/ChangeLog:
2020-05-23  Pedro Alves  <palves@redhat.com>

	* utils.c: Include "gdbsupport/gdb-safe-ctype.h".
	(parse_escape): Use ISDIGIT instead of isdigit.
	(puts_debug): Use gdb_isprint instead of isprint.
	(fprintf_symbol_filtered): Use ISALNUM instead of isalnum.
	(cp_skip_operator_token, skip_ws, strncmp_iw_with_mode): Use
	ISSPACE instead of isspace.
	(strncmp_iw_with_mode): Use TOLOWER instead of tolower and ISSPACE
	instead of isspace.
	(strcmp_iw_ordered): Use ISSPACE instead of isspace.
	(string_to_core_addr): Use TOLOWER instead of tolower, ISXDIGIT
	instead of isxdigit and ISDIGIT instead of isdigit.

gdbsupport/ChangeLog:
2020-05-23  Pedro Alves  <palves@redhat.com>

	* gdb-safe-ctype.h: New.