File handling: Do not abort on seeing a BOM in input files, just warn and ignore the BOM

include/shared.h

@@ -63,6 +63,7 @@ bool hc_path_create (const char *path);
 bool hc_path_has_bom (const char *path);
 
 bool hc_string_is_digit (const char *s);
+int  hc_string_bom_size (const u8 *s);
 
 void hc_string_trim_trailing (char *s);
 void hc_string_trim_leading (char *s);

include/types.h

@@ -1067,9 +1067,11 @@ typedef struct hc_fp
 
   bool        is_gzip;
   bool        is_zip;
+  int         bom_size;
 
   char       *mode;
   const char *path;
+
 } HCFILE;
 
 #include "ext_nvrtc.h"