libbacktrace: avoid void * pointer arithmetic

Git's DEVELOPER CFLAGS do not allow it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

compat/libbacktrace/pecoff.c

@@ -648,7 +648,7 @@ coff_add (struct backtrace_state *state, int descriptor,
       magic_ok = memcmp (magic, "PE\0", 4) == 0;
       fhdr_off += 4;
 
-      memcpy (&fhdr, fhdr_view.data + 4, sizeof fhdr);
+      memcpy (&fhdr, ((char *)fhdr_view.data) + 4, sizeof fhdr);
     }
   else
     {
@@ -682,7 +682,7 @@ coff_add (struct backtrace_state *state, int descriptor,
   sects_view_valid = 1;
   opt_hdr = (const b_coff_optional_header *) sects_view.data;
   sects = (const b_coff_section_header *)
-    (sects_view.data + fhdr.size_of_optional_header);
+    (((char *)sects_view.data) + fhdr.size_of_optional_header);
 
   is_64 = 0;
   if (fhdr.size_of_optional_header > sizeof (*opt_hdr))
@@ -726,7 +726,7 @@ coff_add (struct backtrace_state *state, int descriptor,
 	goto fail;
       syms_view_valid = 1;
 
-      str_size = coff_read4 (syms_view.data + syms_size);
+      str_size = coff_read4 ((unsigned char *)syms_view.data + syms_size);
 
       str_off = syms_off + syms_size;