move to llvm 9

- comp_ctx: add VariableMetadata.llvm_alloca
 - comp_ctx: make VariableMetadataMap use ptrs to VariableMetadata

build.zig

@@ -7,7 +7,7 @@ pub fn build(b: *Builder) void {
     exe.install();
 
     exe.linkSystemLibrary("c");
-    exe.linkSystemLibrary("LLVM-8");
+    exe.linkSystemLibrary("LLVM-9");
     exe.linkSystemLibrary("stdc++");
 
     const run_cmd = exe.run();

src/comp_ctx.zig

@@ -139,6 +139,7 @@ const Using = enum {
 
 pub const VariableMetadata = struct {
     typ: SymbolUnderlyingType,
+    llvm_alloca: llvm.LLVMValueRef = null,
 
     using: Using,
 
@@ -155,7 +156,7 @@ pub const VariableMetadata = struct {
 };
 
 // TODO rm const?
-pub const VariableMetadataMap = std.AutoHashMap(*const ast.Expr, VariableMetadata);
+pub const VariableMetadataMap = std.AutoHashMap(*const ast.Expr, *VariableMetadata);
 
 /// Represents the context for a full compiler run.
 /// This is used to manage the symbol table for the compilation unit, etc.
@@ -380,7 +381,10 @@ pub const CompilationContext = struct {
     }
 
     pub fn insertMetadata(self: *@This(), ptr: *const ast.Expr, metadata: VariableMetadata) !void {
+        var meta = try self.allocator.create(VariableMetadata);
+        meta.* = metadata;
+
         std.debug.assert(ast.ExprType(ptr.*) == .Variable);
-        _ = try self.metadata_map.put(ptr, metadata);
+        _ = try self.metadata_map.put(ptr, meta);
     }
 };