Use path to patch compiler-builtins

.cargo/config

@@ -0,0 +1 @@
+paths = ["compiler-builtins"]

.gitmodules

@@ -13,3 +13,6 @@
 [submodule "pthreads-emb"]
 	path = pthreads-emb
 	url = https://gitlab.redox-os.org/redox-os/pthreads-emb.git
+[submodule "compiler-builtins"]
+	path = compiler-builtins
+	url = https://github.com/rust-lang/compiler-builtins.git

Xargo.toml

@@ -1,4 +1 @@
 [dependencies.alloc]
-
-[patch.crates-io]
-compiler_builtins = { git = "https://github.com/rust-lang/compiler-builtins.git", rev = "25ea08da2824b8137b6ac1222b0171cb07cca083" }

compiler-builtins

@@ -0,0 +1 @@
+Subproject commit 25ea08da2824b8137b6ac1222b0171cb07cca083