Update backtrace for bsd

Author: tesuji

.gitmodules

@@ -46,4 +46,5 @@
 	url = https://github.com/rust-analyzer/rust-analyzer.git
 [submodule "library/backtrace"]
 	path = library/backtrace
-	url = https://github.com/rust-lang/backtrace-rs.git
+	url = https://github.com/lzutao/backtrace-rs.git
+	branch = bsd