io/Open: add `flags` parameter to OpenReadOnly()

src/io/Open.cxx

@@ -34,10 +34,10 @@
 #include <fcntl.h>
 
 UniqueFileDescriptor
-OpenReadOnly(const char *path)
+OpenReadOnly(const char *path, int flags)
 {
 	UniqueFileDescriptor fd;
-	if (!fd.OpenReadOnly(path))
+	if (!fd.Open(path, O_RDONLY|flags))
 		throw FormatErrno("Failed to open '%s'", path);
 
 	return fd;

src/io/Open.hxx

@@ -34,7 +34,7 @@ class FileDescriptor;
 class UniqueFileDescriptor;
 
 UniqueFileDescriptor
-OpenReadOnly(const char *path);
+OpenReadOnly(const char *path, int flags=0);
 
 UniqueFileDescriptor
 OpenWriteOnly(const char *path, int flags=0);