stage1: resolve builtin types and values via std.builtin

rather than via `@import("builtin")`. This helps avoid the need for
`usingnamespace` used in builtin.zig or in std.builtin.

src/stage1/all_types.hpp

@@ -2077,6 +2077,7 @@ struct CodeGen {
     ZigType *compile_var_import;
     ZigType *root_import;
     ZigType *start_import;
+    ZigType *std_builtin_import;
 
     struct {
         ZigType *entry_bool;

src/stage1/analyze.cpp

@@ -8185,14 +8185,18 @@ bool err_ptr_eql(const ErrorTableEntry *a, const ErrorTableEntry *b) {
 }
 
 ZigValue *get_builtin_value(CodeGen *codegen, const char *name) {
-    ScopeDecls *builtin_scope = get_container_scope(codegen->compile_var_import);
-    Tld *tld = find_container_decl(codegen, builtin_scope, buf_create_from_str(name));
+    Buf *buf_name = buf_create_from_str(name);
+
+    ScopeDecls *builtin_scope = get_container_scope(codegen->std_builtin_import);
+    Tld *tld = find_container_decl(codegen, builtin_scope, buf_name);
     assert(tld != nullptr);
     resolve_top_level_decl(codegen, tld, nullptr, false);
     assert(tld->id == TldIdVar && tld->resolution == TldResolutionOk);
     TldVar *tld_var = (TldVar *)tld;
     ZigValue *var_value = tld_var->var->const_value;
     assert(var_value != nullptr);
+
+    buf_destroy(buf_name);
     return var_value;
 }
 

src/stage1/codegen.cpp

@@ -9495,9 +9495,9 @@ static void gen_root_source(CodeGen *g) {
     TldVar *builtin_tld_var = (TldVar*)builtin_tld;
     ZigValue *builtin_val = builtin_tld_var->var->const_value;
     assert(builtin_val->type->id == ZigTypeIdMetaType);
-    ZigType *builtin_type = builtin_val->data.x_type;
+    g->std_builtin_import = builtin_val->data.x_type;
 
-    Tld *panic_tld = find_decl(g, &get_container_scope(builtin_type)->base,
+    Tld *panic_tld = find_decl(g, &get_container_scope(g->std_builtin_import)->base,
             buf_create_from_str("panic"));
     assert(panic_tld != nullptr);
     resolve_top_level_decl(g, panic_tld, nullptr, false);