Test the unsafe_extern_blocks feature

Author: pvdrz

bindgen-tests/tests/expectations/tests/extern_blocks_post_1_82.rs

@@ -0,0 +1,5 @@
+// bindgen-flags: --no-layout-tests --rust-target=1.82
+
+void cool_function(int i, char c);
+
+static int cool_static;

bindgen-tests/tests/expectations/tests/extern_blocks_pre_1_82.rs

@@ -0,0 +1,5 @@
+// bindgen-flags: --no-layout-tests --rust-target=1.81
+
+void cool_function(int i, char c);
+
+static int cool_static;