Add wrappers around fopen(), use mmap on glibc

Add wrappers to fopen().  The intent is to replace references to
FILE * with an internal structure which can also cache things like the
filename and, when needed, the full pathname and checksums.

Also, add the "m" flag if we are compiling for glibc, for speed.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

output/codeview.c

@@ -341,7 +341,7 @@ static void calc_md5(const char *const filename,
     FILE *f;
     MD5_CTX ctx;
 
-    f = pp_input_fopen(filename, "rb");
+    f = pp_input_fopen(filename, NF_BINARY);
     if (!f)
         goto done;