libbacktrace: avoid -Wpointer-arith errors

Based on patch from Kirill Müller.

	* configure.ac (ACX_PROG_CC_WARNING_OPTS): Add -Wpointer-arith.
	* pecoff.c (coff_add): Cast void pointers.
	* xcoff.c (xcoff_add): Likewise.
	* configure: Regenerate.

libbacktrace/configure

@@ -12385,7 +12385,8 @@ save_CFLAGS="$CFLAGS"
 for real_option in -W -Wall -Wwrite-strings -Wstrict-prototypes \
 			  -Wmissing-prototypes -Wold-style-definition \
 			  -Wmissing-format-attribute -Wcast-qual \
-			  -Wno-attributes -Wno-unknown-attributes; do
+			  -Wno-attributes -Wno-unknown-attributes \
+			  -Wpointer-arith; do
   # Do the check with the no- prefix removed since gcc silently
   # accepts any -Wno-* option on purpose
   case $real_option in

libbacktrace/configure.ac

@@ -145,7 +145,8 @@ AC_SUBST(EXTRA_FLAGS)
 ACX_PROG_CC_WARNING_OPTS([-W -Wall -Wwrite-strings -Wstrict-prototypes \
 			  -Wmissing-prototypes -Wold-style-definition \
 			  -Wmissing-format-attribute -Wcast-qual \
-			  -Wno-attributes -Wno-unknown-attributes],
+			  -Wno-attributes -Wno-unknown-attributes \
+			  -Wpointer-arith],
 			  [WARN_FLAGS])
 
 AC_ARG_ENABLE([werror],

libbacktrace/pecoff.c

@@ -704,7 +704,7 @@ 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, (const unsigned char *) fhdr_view.data + 4, sizeof fhdr);
     }
   else
     {
@@ -738,7 +738,7 @@ 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);
+    ((const unsigned char *) sects_view.data + fhdr.size_of_optional_header);
 
   is_64 = 0;
   memset (&image_base, 0, sizeof image_base);
@@ -781,7 +781,8 @@ 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 ((const unsigned char *) syms_view.data
+			     + syms_size);
 
       str_off = syms_off + syms_size;
 

libbacktrace/xcoff.c

@@ -1203,7 +1203,9 @@ xcoff_add (struct backtrace_state *state, int descriptor, off_t offset,
 	goto fail;
       syms_view_valid = 1;
 
-      memcpy (&str_size, syms_view.data + syms_size, 4);
+      memcpy (&str_size,
+	      (const unsigned char *) syms_view.data + syms_size,
+	      4);
 
       str_off = fhdr.f_symptr + syms_size;