cblas: typedef enums for improved compatibility with Intel MKL.

Netlib style:
    enum CBLAS_XYZ {X=1, Y=2, Z=3};

Intel MKL style:
    typedef enum {X=1, Y=2, Z=3} CBLAS_XYZ;

With this hybrid style, code written in the latter form won't need any
modifications to be built with OpenBLAS.  This change should not affect existing
code, although a warning may be emitted for C code which does the following
(does not occur with C++):
    typedef enum CBLAS_XYZ CBLAS_XYZ;
    warning: redefinition of typedef 'CBLAS_XYZ' [-pedantic]