[Bug-gsl] fix for a broken complex macro from MSVC headers

[address@hidden]

I had a compilation error when trying to build GSL with Visual C++. The
problem was that the math.h supplied with this compiler redefines complex
as _complex thus messing up the concatenated names in the GSL matrix
library, for example, gsl_matrix__complex_submatrix (note double "_"
between matrix and complex).

The attached trivial patch fixes the problem by undefining complex in
templates_on.h

Best regards,
Victor

0001-Undefine-complex.patch
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