Auto-import std::core. Fix module assignment of declarations. Introspection improvements. Deref null error panics in safe mode. Support for LLVM 15

test/test_suite2/bitstruct/bitstruct_single_error.c3

@@ -0,0 +1,19 @@
+bitstruct Foo1 : char
+{
+    char x : 1..1;
+}
+
+bitstruct Foo2 : char
+{
+    char x : 1; // #error: Only booleans may use non-range indices
+}
+
+bitstruct Foo3 : char
+{
+    bool x : 0..2; // #error: The bit width of 'bool'
+}
+
+bitstruct Foo4 : int
+{
+    char x : 0..15; // #error: The bit width of 'char'
+}