wasm: fix crash when qtvkb tries to load a plugin

We do not have dlopen, harfbuzz seems to try and load the thai
plugin using dlopen when just iterating through the language
selector in virtualkeyboard..

Fixes: QTBUG-78825
Change-Id: Iee064a1d9a628784e3ce46d641cd157a69bcb696
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/corelib/text/qharfbuzz.cpp

@@ -72,7 +72,7 @@ HB_UChar16 HB_GetMirroredChar(HB_UChar16 ch)
 
 void (*HB_Library_Resolve(const char *library, int version, const char *symbol))()
 {
-#if !QT_CONFIG(library)
+#if !QT_CONFIG(library) || defined(Q_OS_WASM)
     Q_UNUSED(library);
     Q_UNUSED(version);
     Q_UNUSED(symbol);