Sema: do not immediately destroy failed generic instantiation

Closes #12535
Closes #12765
Closes #12927

test/cases/compile_errors/error_in_comptime_call_in_container_level_initializer.zig

@@ -0,0 +1,22 @@
+const std = @import("std");
+const Version = std.SemanticVersion;
+const print = @import("std").debug.print;
+
+fn readVersion() Version {
+    const version_file = "foo";
+    const len = std.mem.indexOfAny(u8, version_file, " \n") orelse version_file.len;
+    const version_string = version_file[0..len];
+    return Version.parse(version_string) catch unreachable;
+}
+
+const version: Version = readVersion();
+pub export fn entry() void {
+    print("Version {}.{}.{}+{?s}\n", .{ version.major, version.minor, version.patch, version.build });
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :9:48: error: caught unexpected error 'InvalidVersion'
+// :12:37: note: called from here

test/cases/compile_errors/generic_instantiation_failure.zig

@@ -0,0 +1,27 @@
+fn List(comptime Head: type, comptime Tail: type) type {
+    return union {
+        const Self = @This();
+        head: Head,
+        tail: Tail,
+
+        fn AppendReturnType(comptime item: anytype) type {
+            return List(Head, List(@TypeOf(item), void));
+        }
+    };
+}
+
+fn makeList(item: anytype) List(@TypeOf(item), void) {
+    return List(@TypeOf(item), void){ .head = item };
+}
+
+pub export fn entry() void {
+    @TypeOf(makeList(42)).AppendReturnType(64);
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :18:43: error: value of type 'type' ignored
+// :18:43: note: all non-void values must be used
+// :18:43: note: this error can be suppressed by assigning the value to '_'

test/cases/compile_errors/generic_instantiation_failure_in_generic_function_return_type.zig

@@ -0,0 +1,14 @@
+const std = @import("std");
+
+pub export fn entry() void {
+    var ohnoes: *usize = undefined;
+    _ = sliceAsBytes(ohnoes);
+}
+fn sliceAsBytes(slice: anytype) std.meta.trait.isPtrTo(.Array)(@TypeOf(slice)) {}
+
+
+// error
+// backend=llvm
+// target=native
+//
+// :7:63: error: expected type 'type', found 'bool'