internal/syscall/windows/registry: append .dll when loading kernel32

Win32 LoadLibrary supports loading a DLL omitting the .dll extension,
but it is better to be explicit and include the extension. This is
consistent with all other uses of LoadLibrary in the Go standard
library.

Change-Id: I7349d0a27db5f8ab59061434f37d10918e43b869
Reviewed-on: https://go-review.googlesource.com/c/go/+/569535
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: qmuntal

src/internal/syscall/windows/registry/registry_test.go

@@ -647,9 +647,9 @@ type DynamicTimezoneinformation struct {
 }
 
 var (
-	kernel32DLL = syscall.NewLazyDLL("kernel32")
+	modkernel32 = syscall.NewLazyDLL("kernel32.dll")
 
-	procGetDynamicTimeZoneInformation = kernel32DLL.NewProc("GetDynamicTimeZoneInformation")
+	procGetDynamicTimeZoneInformation = modkernel32.NewProc("GetDynamicTimeZoneInformation")
 )
 
 func GetDynamicTimeZoneInformation(dtzi *DynamicTimezoneinformation) (rc uint32, err error) {