Adds a modified f2c-generated C implmentation for BLAS.

This adds an optional implementation for the BLAS library that does
not require the use of a FORTRAN compiler. It can be enabled with
EIGEN_USE_F2C_BLAS.

The C implementation uses the standard gfortran calling convention
and does not require the use of -ff2c when compiled with gfortran.

blas/f2c/datatypes.h

@@ -0,0 +1,24 @@
+/* This contains a limited subset of the typedefs exposed by f2c
+   for use by the Eigen BLAS C-only implementation.
+*/
+
+#ifndef __EIGEN_DATATYPES_H__
+#define __EIGEN_DATATYPES_H__
+
+typedef int integer;
+typedef unsigned int uinteger;
+typedef float real;
+typedef double doublereal;
+typedef struct { real r, i; } complex;
+typedef struct { doublereal r, i; } doublecomplex;
+typedef int ftnlen;
+typedef int logical;
+
+#define abs(x) ((x) >= 0 ? (x) : -(x))
+#define dabs(x) (doublereal)abs(x)
+#define min(a,b) ((a) <= (b) ? (a) : (b))
+#define max(a,b) ((a) >= (b) ? (a) : (b))
+#define dmin(a,b) (doublereal)min(a,b)
+#define dmax(a,b) (doublereal)max(a,b)
+
+#endif