Support C-Style enum in preproc (#1984)

* [preproc] C-style enums

- asm files parseable from stdin
- 2nd preproc pass
- add parser for C-style `enum`
- positional arguments at end of command

---------

Co-authored-by: sbird <sbird@no.tld>
Co-authored-by: Martin Griffin <martinrgriffin@gmail.com>

tools/preproc/Makefile

@@ -3,10 +3,10 @@ CXX ?= g++
 CXXFLAGS := -std=c++11 -O2 -Wall -Wno-switch -Werror
 
 SRCS := asm_file.cpp c_file.cpp charmap.cpp preproc.cpp string_parser.cpp \
-	utf8.cpp
+	utf8.cpp io.cpp
 
 HEADERS := asm_file.h c_file.h char_util.h charmap.h preproc.h string_parser.h \
-	utf8.h
+	utf8.h io.h
 
 ifeq ($(OS),Windows_NT)
 EXE := .exe