Style field names in "print"

Style field names in "print"

This changes gdb to use the "variable" style when printing field
names.  I've added new tests for C and Rust, but not other languages.

I chose "variable" because that seemed most straightforward.  However,
another option would be to introduce a new "field" style.  Similarly,
this patch uses the variable style for enumerator constants -- but
again, a new style could be used if that's preferred.

gdb/ChangeLog
2020-02-22  Tom Tromey  <tom@tromey.com>

	* valprint.c (generic_val_print_enum_1)
	(val_print_type_code_flags): Style member names.
	* rust-lang.c (val_print_struct, rust_print_enum)
	(rust_print_struct_def, rust_internal_print_type): Style member
	names.
	* p-valprint.c (pascal_object_print_value_fields): Style member
	names.  Only call fprintf_symbol_filtered for static members.
	* m2-typeprint.c (m2_record_fields, m2_enum): Style member names.
	* f-valprint.c (f_val_print): Style member names.
	* f-typeprint.c (f_type_print_base): Style member names.
	* cp-valprint.c (cp_print_value_fields): Style member names.  Only
	call fprintf_symbol_filtered for static members.
	(cp_print_class_member): Style member names.
	* c-typeprint.c (c_print_type_1, c_type_print_base_1): Style
	member names.
	* ada-valprint.c (ada_print_scalar): Style enum names.
	(ada_val_print_enum): Likewise.
	* ada-typeprint.c (print_enum_type): Style enum names.

gdb/testsuite/ChangeLog
2020-02-22  Tom Tromey  <tom@tromey.com>

	* gdb.rust/rust-style.rs: New file.
	* gdb.rust/rust-style.exp: New file.
	* gdb.base/style.exp: Test structure printing.
	* gdb.base/style.c (struct some_struct): New type.
	(enum etype): New type.
	(struct_value): New global.

Change-Id: I070e1293c6cc830c9ea916af8243410aa384e944