Add optimizations for QJSValue tests for MSVC.

The comment is not valid. It was added for QScriptValue generated test
which are not included in QJSValue tests.

Change-Id: I958e3c1d1f57cfa0ad34d1a8c8387deec792efaf
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>

tests/auto/declarative/qjsvalue/qjsvalue.pro

@@ -4,9 +4,3 @@ macx:CONFIG -= app_bundle
 QT += declarative widgets testlib
 SOURCES  += tst_qjsvalue.cpp
 HEADERS  += tst_qjsvalue.h
-
-win32-msvc* {
-    # With -O2, MSVC takes up to 24 minutes to compile this test!
-    QMAKE_CXXFLAGS_RELEASE -= -O1 -O2
-    QMAKE_CXXFLAGS_RELEASE += -Od
-}