This enables -Wpointer-sign by default.
I've checked that --enable-targets=all builds fine with the following
as --host, on x86_64 Fedora 17 --build:
x86_64 GNU/Linux
i386 GNU/Linux
i386 MinGW-w64
i386 msdos/djgpp
OK?
gdb/
2013-04-19  Pedro Alves  <palves@redhat.com>
	* configure.ac (build_warnings): Replace -Wno-pointer-sign with
	-Wpointer-sign.
	* configure: Regenerate.
gdb/doc
2013-04-19  Pedro Alves  <palves@redhat.com>
	* gdbint.texinfo (Misc Guidelines) <Compiler Warnings>: Replace
	-Wno-pointer-sign text with text on -Wpointer-sign.
+2013-04-19  Pedro Alves  <palves@redhat.com>
+
+       * configure.ac (build_warnings): Replace -Wno-pointer-sign with
+       -Wpointer-sign.
+       * configure: Regenerate.
+
 2013-04-19  Pedro Alves  <palves@redhat.com>
 
        * ser-tcp.c (net_read_prim): Cast second argument to recv to
 
 # NOTE: If you change this list, remember to update
 # gdb/doc/gdbint.texinfo.
 build_warnings="-Wall -Wdeclaration-after-statement -Wpointer-arith \
--Wformat-nonliteral -Wno-pointer-sign \
+-Wformat-nonliteral -Wpointer-sign \
 -Wno-unused -Wunused-value -Wunused-function \
 -Wno-switch -Wno-char-subscripts -Wmissing-prototypes \
 -Wdeclaration-after-statement -Wempty-body"
 
 # NOTE: If you change this list, remember to update
 # gdb/doc/gdbint.texinfo.
 build_warnings="-Wall -Wdeclaration-after-statement -Wpointer-arith \
--Wformat-nonliteral -Wno-pointer-sign \
+-Wformat-nonliteral -Wpointer-sign \
 -Wno-unused -Wunused-value -Wunused-function \
 -Wno-switch -Wno-char-subscripts -Wmissing-prototypes \
 -Wdeclaration-after-statement -Wempty-body"
 
+2013-04-19  Pedro Alves  <palves@redhat.com>
+
+       * gdbint.texinfo (Misc Guidelines) <Compiler Warnings>: Replace
+       -Wno-pointer-sign text with text on -Wpointer-sign.
+
 2013-04-16  Tom Tromey  <tromey@redhat.com>
 
        * gdb.texinfo (Set Catchpoints): Mention earliest version of
 
 @code{printf} like functions this checks not just @code{printf} calls
 but also calls to functions such as @code{fprintf_unfiltered}.
 
-@item -Wno-pointer-sign
-In version 4.0, GCC began warning about pointer argument passing or
-assignment even when the source and destination differed only in
-signedness.  However, most @value{GDBN} code doesn't distinguish
-carefully between @code{char} and @code{unsigned char}.  In early 2006
-the @value{GDBN} developers decided correcting these warnings wasn't
-worth the time it would take.
+@item -Wpointer-sign
+This helps make sure @value{GDBN} code uses @code{gdb_byte} which is
+really @code{unsigned char} for raw bytes instead of @code{char},
+whose signness is host-dependent.  @sc{gcc} enables this with
+@code{-Wall} since version 4.0.  We enable it explicitly too to be
+decoupled from future @sc{gcc} (or other compiler)'s defaults.
 
 @item -Wno-unused-parameter
 Due to the way that @value{GDBN} is implemented many functions have