Make map_file_from_path use the open flags

map_file_from_path now passes the appropriate flags on to os.open
instead of always calling it with os.O_RDWR.
It will no longer try to open a file with write permissions if the user
didn't request write access to the file mapping (or vice-versa).

core/mem/virtual/file.odin

@@ -10,7 +10,14 @@ map_file :: proc{
 }
 
 map_file_from_path :: proc(filename: string, flags: Map_File_Flags) -> (data: []byte, error: Map_File_Error) {
-	f, err := os.open(filename, os.O_RDWR)
+	open_flags : os.File_Flags
+	if .Read in flags {
+		open_flags += {.Read}
+	}
+	if .Write in flags {
+		open_flags += {.Write}
+	}
+	f, err := os.open(filename, open_flags)
 	if err != nil {
 		return nil, .Open_Failure
 	}
@@ -37,4 +44,4 @@ unmap_file :: proc(data: []byte) {
 	if raw_data(data) != nil {
 		_unmap_file(data)
 	}
-}
+}