Revert "Switch to using std::filesystem (#1235)"

This reverts commit cf62ff772f.
Some functions used by this break on macOS before 10.15,
which we want to keep supporting.

include/file.hpp

@@ -7,7 +7,6 @@
 #include <assert.h>
 #include <cassert>
 #include <fcntl.h>
-#include <filesystem>
 #include <fstream>
 #include <ios>
 #include <iostream>
@@ -42,7 +41,7 @@ public:
 	 * This should only be called once, and before doing any `->` operations.
 	 * Returns `nullptr` on error, and a non-null pointer otherwise.
 	 */
-	File *open(std::filesystem::path const &path, std::ios_base::openmode mode) {
+	File *open(std::string const &path, std::ios_base::openmode mode) {
 		if (path != "-") {
 			return _file.emplace<std::filebuf>().open(path, mode) ? this : nullptr;
 		} else if (mode & std::ios_base::in) {
@@ -86,11 +85,11 @@ public:
 		           : nullptr;
 	}
 
-	std::string string(std::filesystem::path const &path) const {
-		return std::visit(Visitor{[&path](std::filebuf const &) { return path.string(); },
+	char const *c_str(std::string const &path) const {
+		return std::visit(Visitor{[&path](std::filebuf const &) { return path.c_str(); },
 		                          [](std::streambuf const *buf) {
-			                          return std::string{buf == std::cin.rdbuf()
-			                                 ? "<stdin>" : "<stdout>"};
+			                          return buf == std::cin.rdbuf()
+			                                 ? "<stdin>" : "<stdout>";
 		                          }},
 		                  _file);
 	}

include/gfx/main.hpp

@@ -4,9 +4,7 @@
 #define RGBDS_GFX_MAIN_HPP
 
 #include <array>
-#include <filesystem>
 #include <limits.h>
-#include <optional>
 #include <stdint.h>
 #include <string>
 #include <utility>
@@ -26,7 +24,7 @@ struct Options {
 	bool columnMajor = false; // -Z, previously -h
 	uint8_t verbosity = 0; // -v
 
-	std::optional<std::filesystem::path> attrmap{}; // -a, -A
+	std::string attrmap{}; // -a, -A
 	std::array<uint8_t, 2> baseTileIDs{0, 0}; // -b
 	enum {
 		NO_SPEC,
@@ -43,14 +41,14 @@ struct Options {
 	} inputSlice{0, 0, 0, 0}; // -L (margins in clockwise order, like CSS)
 	std::array<uint16_t, 2> maxNbTiles{UINT16_MAX, 0}; // -N
 	uint8_t nbPalettes = 8; // -n
-	std::optional<std::filesystem::path> output{}; // -o
-	std::optional<std::filesystem::path> palettes{}; // -p, -P
-	std::optional<std::filesystem::path> palmap{}; // -q, -Q
+	std::string output{}; // -o
+	std::string palettes{}; // -p, -P
+	std::string palmap{}; // -q, -Q
 	uint8_t nbColorsPerPal = 0; // -s; 0 means "auto" = 1 << bitDepth;
-	std::optional<std::filesystem::path> tilemap{}; // -t, -T
+	std::string tilemap{}; // -t, -T
 	uint64_t trim = 0; // -x
 
-	std::optional<std::filesystem::path> input{}; // positional arg
+	std::string input{}; // positional arg
 
 	static constexpr uint8_t VERB_NONE = 0; // Normal, no extra output
 	static constexpr uint8_t VERB_CFG = 1; // Print configuration after parsing options