Use const pointers for arguments of type [in] headers

[dhermes]

See lapack.h for an example already in use, for example

#define LAPACK_dgetrf LAPACK_GLOBAL(dgetrf,DGETRF)
void LAPACK_dgetrf(
    lapack_int const* m, lapack_int const* n,
    double* A, lapack_int const* lda, lapack_int* ipiv,
    lapack_int* info );

has marked m, n and lda constant which matches the [in] arguments from the docs

I went with the macro-less

extern void dgetrf_(const int* M, const int* N, double* A, const int* LDA,
    int* IPIV, int* INFO);

in a blog post about LAPACK.

[dhermes]

As some other prior art, the Intel MKL docs on their LAPACK interface says

The arguments of the C interfaces for the Intel MKL LAPACK functions comply with the following rules:

• Scalar input arguments are passed by value.
• Array arguments are passed by reference.
• Array input arguments are declared with the const modifier.

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