[PROPOSAL] Drop the pre-C99 types (at least from internal code)

[derobins]

PROBLEM

The HDF4 library was created in a pre-C99 world and contains a type system that mimics C-99 fixed-size integer types, etc. It would be nice to replace this with C-99 types, at least internally.

The list of types (from hdf/src/hdfi.h):

/* Floating-point types */                                                       
typedef float  float32;                                                          
typedef double float64;                                                          
                                                                                 
/* Characters */                                                                 
typedef char          char8;                                                     
typedef unsigned char uchar8;                                                    
typedef char         *_fcd;                                                      
#define _fcdtocp(desc) (desc)                                                    
                                                                                 
/* Fixed-width integer types */                                                  
typedef int8_t   int8;                                                           
typedef uint8_t  uint8;                                                          
typedef int16_t  int16;                                                          
typedef uint16_t uint16;                                                         
typedef int32_t  int32;                                                          
typedef uint32_t uint32;                                                         
                                                                                 
/* Native integer types */                                                       
typedef int          intn;                                                       
typedef unsigned int uintn;                                                      
                                                                                 
/* These are no longer used in the library, but other software uses them */      
#ifndef VOID                                                                     
/* winnt.h defines VOID to `void` via a macro */                                 
typedef void VOID;                                                               
#endif                                                                           
typedef void *VOIDP;  

PROPOSED FIX

• In non-public headers and all source code, the C-99 types would replace the HDF4 scheme.
• The public API could also be updated, but this might cause confusion. If we did this, we'd also have to update the documentation, which would be a chore.
• The existing HDF4 typedef scheme would be moved to the public API for compatibility with software that needs it. This could be protected by ifdefs and configure options if desired.

HOW WOULD USERS BE AFFECTED?

PRO
➕ HDF4 library code looks like modern C code
➕ Old-school things available for software that needs it
➕ No documentation or API changes if the public API is unchanged

CON
➖ Possible user confusion if we update the public API
➖ Documentation changes if we update the public API
➖Library might look "binary incompatible" if we update the public API, even though the types would be equivalent

NEUTRAL
✔️ Might want to add options to hide legacy types