Standardize on using / for all paths.

Without this change there is no cross-platform way to create a
directory on Windows, since the previous code checked for the
path delimiter as the final character, which was OS-dependent.

Seems to work on Windows based on tbsp's testing.

This change also fixes realpath on Windows.

Suggested by tbsp, based on:

https://stackoverflow.com/questions/45124869/cross-platform-alternative-to-this-realpath-definition/72492046#72492046

src/devices/file.c

@@ -8,27 +8,30 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#ifdef _WIN32
-#include <direct.h>
-#include <libiberty/libiberty.h>
-#define realpath(s, dummy) lrealpath(s)
-#define DIR_SEP_CHAR '\\'
-#define DIR_SEP_STR "\\"
-#define pathcmp(path1, path2, length) strncasecmp(path1, path2, length) /* strncasecmp provided by libiberty */
-#define notdriveroot(file_name) (file_name[0] != DIR_SEP_CHAR && ((strlen(file_name) > 2 && file_name[1] != ':') || strlen(file_name) <= 2))
-#define mkdir(file_name) (_mkdir(file_name) == 0)
-#else
-#define DIR_SEP_CHAR '/'
-#define DIR_SEP_STR "/"
-#define pathcmp(path1, path2, length) strncmp(path1, path2, length)
-#define notdriveroot(file_name) (file_name[0] != DIR_SEP_CHAR)
-#define mkdir(file_name) (mkdir(file_name, 0755) == 0)
-#endif
-
 #ifndef PATH_MAX
 #define PATH_MAX 4096
 #endif
 
+/* Windows devices can handle relative paths like "abc/def.txt" and
+   absolute paths like "/foo/bar/baz.txt" so cross-platform ROMs
+   should just use forward slash unconditionally and let the emulator
+   worry about how to find the files in the filesystem. */
+
+#ifdef _WIN32
+#include <direct.h>
+#include <libiberty/libiberty.h>
+#define realpath(s, dummy) _fullpath((dummy), (s), PATH_MAX)
+#define pathcmp(path1, path2, length) strncasecmp(path1, path2, length)
+#define mkdir(file_name) (_mkdir(file_name) == 0)
+#else
+#define pathcmp(path1, path2, length) strncmp(path1, path2, length)
+#define mkdir(file_name) (mkdir(file_name, 0755) == 0)
+#endif
+
+#define DIR_SEP_CHAR '/'
+#define DIR_SEP_STR "/"
+#define notdriveroot(file_name) (file_name[0] != DIR_SEP_CHAR)
+
 #include "../uxn.h"
 #include "file.h"
 
@@ -140,20 +143,19 @@ retry_realpath(const char *file_name)
 		return NULL;
 	}
 	if(notdriveroot(file_name)) {
-		/* TODO: use a macro instead of '/' for absolute path first character so that other systems can work */
 		/* if a relative path, prepend cwd */
 		getcwd(p, sizeof(p));
 		if(strlen(p) + strlen(DIR_SEP_STR) + fnlen >= PATH_MAX) {
 			errno = ENAMETOOLONG;
 			return NULL;
 		}
-		strcat(p, DIR_SEP_STR); /* TODO: use a macro instead of '/' for the path delimiter */
+		strcat(p, DIR_SEP_STR);
 	}
 	strcat(p, file_name);
 	while((r = realpath(p, NULL)) == NULL) {
 		if(errno != ENOENT)
 			return NULL;
-		x = strrchr(p, DIR_SEP_CHAR); /* TODO: path delimiter macro */
+		x = strrchr(p, DIR_SEP_CHAR);
 		if(x)
 			*x = '\0';
 		else
@@ -217,19 +219,19 @@ is_dir_path(char *p)
 {
 	char c;
 	int saw_slash = 0;
-	while (c = *p++)
+	while ((c = *p++))
 		saw_slash = c == DIR_SEP_CHAR;
 	return saw_slash;
 }
 
-int
+static int
 dir_exists(char *p)
 {
 	struct stat st;
 	return stat(p, &st) == 0 && S_ISDIR(st.st_mode);
 }
 
-int
+static int
 ensure_parent_dirs(char *p)
 {
 	int ok = 1;