math(EXPR) does not parse unary negation properly

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

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MATH(EXPR varOutput "-1 + 1")

gives an error:

CMake Error at CMakeLists.txt:1 (MATH):
  math cannot parse the expression: "-1 + 1": syntax error, unexpected
  exp_MINUS, expecting exp_OPENPARENT or exp_NUMBER (1)

I think +1 + 1 also does not work.