Add few compile errors test cases

test/cases/compile_errors/callconv_inline.zig

@@ -0,0 +1,5 @@
+inline fn entry() callconv(.c) void {}
+
+// error
+//
+// :1:29: error: explicit callconv incompatible with inline keyword

test/cases/compile_errors/decl_literal_must_be_compile_known.zig

@@ -0,0 +1,31 @@
+pub const X = enum {
+    var foo: X = .field;
+    var undef: X = undefined;
+
+    field,
+};
+
+pub const Y = enum {
+    var undef: Y = undefined;
+
+    field,
+    field2,
+};
+
+export fn entry() void {
+    {
+        const foo: X = .foo; // works since X.foo is of type X (enum with only one field).
+        _ = foo;
+    }
+    {
+        const foo: X = .undef; // works since X.undef is of type X (enum with only one field).
+        _ = foo;
+    }
+    {
+        const foo: Y = .undef;
+        _ = foo;
+    }
+}
+// error
+//
+// :25:25: error: decl literal must be comptime-known

test/cases/compile_errors/decl_literal_must_be_compile_known2.zig

@@ -0,0 +1,16 @@
+pub const Y = enum {
+    var foo: Y = .field;
+
+    field,
+    field2,
+};
+
+export fn entry() void {
+    {
+        const foo: Y = .foo;
+        _ = foo;
+    }
+}
+// error
+//
+// :10:25: error: decl literal must be comptime-known

test/cases/compile_errors/extern_no_initializer.zig

@@ -0,0 +1,6 @@
+extern var foo = 1;
+extern const bar = 2;
+// error
+//
+// :1:18: error: extern variables have no initializers
+// :2:20: error: extern variables have no initializers

test/cases/compile_errors/function_prototype_inferred_error_set.zig

@@ -0,0 +1,4 @@
+extern fn entry1() !void;
+// error
+//
+// 1:20: error: function prototype may not have inferred error set

test/cases/compile_errors/non_packed_struct_backing.zig

@@ -0,0 +1,4 @@
+const T = struct(u8) {};
+// error
+//
+// :1:18: error: non-packed struct does not support backing integer type

test/cases/compile_errors/variable_missing_value.zig

@@ -0,0 +1,11 @@
+const a;
+const b: u32;
+
+var c;
+var d: u32;
+// error
+//
+// :1:1: error: variables must be initialized
+// :2:1: error: variables must be initialized
+// :4:1: error: variables must be initialized
+// :5:1: error: variables must be initialized