headers: fail Build on missing native exports and assert MI/COM layouts (#2739)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/headers/wtsapi32/wtsapi32.go

@@ -22,9 +22,14 @@ import (
 	"log/slog"
 	"unsafe"
 
+	"github.com/prometheus-community/windows_exporter/internal/headers/lazyproc"
 	"golang.org/x/sys/windows"
 )
 
+// Load checks that wtsapi32.dll exports every function of this package. Call
+// it in Build: a missing export panics on the first call otherwise.
+func Load() error { return load() }
+
 type WTSTypeClass int
 
 // The valid values for the WTSTypeClass enumeration.
@@ -107,6 +112,8 @@ var (
 	procWTSFreeMemoryEx        = wtsapi32.NewProc("WTSFreeMemoryExW")
 	procWTSCloseServer         = wtsapi32.NewProc("WTSCloseServer")
 
+	load = lazyproc.Once(wtsapi32, procWTSOpenServerEx, procWTSEnumerateSessionsEx, procWTSFreeMemoryEx, procWTSCloseServer)
+
 	WTSSessionStates = map[WTSConnectState]string{
 		wtsActive:       "active",
 		wtsConnected:    "connected",