qmake fails to generate moc_*.cpp files on windows if project path contains white spaces when include directives are more than 40

When the following conditions are both met:

• Project path contains white-spaces (for example C:\User Data\workspace\MyProject)
• Include directives are more than 40

Build fails when invoking moc.exe with the following error:

moc: Cannot open options file specified with @

NMAKE : fatal error U1077: 'C:\Qt\5.9.1\msvc2015_64\bin\moc.exe' : return code '0x1'

This is due to qmake generating an invalid command for any moc cpp that has to be generated, for example:

C:\Qt\5.9.1\msvc2015_64\bin\moc.exe $(DEFINES) --compiler-flavor=msvc --include "C:\User Data\workspace\MyProject\moc_predefs.h" @C:\User Data\workspace\MyProject\mocinclude.opt MyQObject.h -o moc_MyQObject.cpp

In this extract from my Makefile, the mocinclude.opt file (which is generated by qmake) is passed to moc.exe without quotes, generating the error above.