change CEED_EPSILON to true constant to appease bindgen

Author: zatkins-dev

include/ceed/ceed-f32.h

@@ -18,4 +18,4 @@ typedef float      CeedScalar;
 typedef CeedScalar CeedScalarCPU;
 
 /// Machine epsilon
-#define CEED_EPSILON 0x1p-23
+static const CeedScalar CEED_EPSILON = 0x1p-23;

include/ceed/ceed-f64.h

@@ -19,11 +19,11 @@ typedef float  CeedScalar;
 typedef double CeedScalarCPU;
 
 /// Machine epsilon
-#define CEED_EPSILON 0x1p-23
+static const CeedScalar CEED_EPSILON = 0x1p-23;
 #else
 typedef double     CeedScalar;
 typedef CeedScalar CeedScalarCPU;
 
 /// Machine epsilon
-#define CEED_EPSILON 0x1p-52
+static const CeedScalar CEED_EPSILON = 0x1p-52;
 #endif  // CEED_RUNNING_JIT_PASS && CEED_JIT_MIXED_PRECISION