Revert "qmake: Work around MSVC compiler bug."

The fix was for MSVC2010 which is now no longer supported
and causes a warning:

msvc_vcproj.cpp(217,12):  warning: unknown pragma ignored [-Wunknown-pragmas]
 #pragma optimize( "g", off )

by clang-cl.

This reverts commit 9f54846.

Task-number: QTBUG-63512
Change-Id: I395b964d09ac04a7dc852e43d7d95669948eea52
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Miguel Costa <miguel.costa@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

qmake/generators/win32/msvc_vcproj.cpp

@@ -208,16 +208,6 @@ struct VcsolutionDepend {
     QStringList dependencies;
 };
 
-/* Disable optimization in getProjectUUID() due to a compiler
- * bug in MSVC 2010 that causes ASSERT: "&other != this" in the QString
- * copy constructor for non-empty file names at:
- * filename.isEmpty()?project->first("QMAKE_MAKEFILE"):filename */
-
-#ifdef Q_CC_MSVC
-#   pragma optimize( "g", off )
-#   pragma warning ( disable : 4748 )
-#endif
-
 QUuid VcprojGenerator::getProjectUUID(const QString &filename)
 {
     bool validUUID = true;
@@ -249,10 +239,6 @@ QUuid VcprojGenerator::getProjectUUID(const QString &filename)
     return uuid;
 }
 
-#ifdef Q_CC_MSVC
-#   pragma optimize( "g", on )
-#endif
-
 QUuid VcprojGenerator::increaseUUID(const QUuid &id)
 {
     QUuid result(id);